JME

JME expressions are used by students to enter answers to algebraic questions, and by question authors to define variables. JME syntax is similar to what you’d type on a calculator.

Variable names

Variable names are case-insensitive, so y represents the same thing as Y. The first character of a variable name must be an alphabet letter; after that, any combination of letters, numbers and underscores is allowed, with any number of ' on the end.

Examples:
  • x
  • x_1
  • time_between_trials
  • var1
  • row1val2
  • y''

e, i and pi are reserved names representing mathematical constants. They are rewritten by the interpreter to their respective numerical values before evaluation.

This screencast describes which variable names are valid, and gives some advice on how you should pick names:

Variable name annotations

Names can be given annotations to change how they are displayed. The following annotations are built-in:

  • verb – does nothing, but names like i, pi and e are not interpreted as the famous mathematical constants.
  • op – denote the name as the name of an operator — wraps the name in the LaTeX operatorname command when displayed
  • v or vector – denote the name as representing a vector — the name is displayed in boldface
  • unit – denote the name as representing a unit vector — places a hat above the name when displayed
  • dot – places a dot above the name when displayed, for example when representing a derivative
  • m or matrix – denote the name as representing a matrix — displayed using a non-italic font

Any other annotation is taken to be a LaTeX command. For example, a name vec:x is rendered in LaTeX as \vec{x}, which places an arrow above the name.

You can apply multiple annotations to a single variable. For example, v:dot:x produces a bold x with a dot on top: \(\boldsymbol{\dot{x}}\).

Data types

number

Numbers include integers, real numbers and complex numbers. There is only one data type for all numbers.

i, e, infinity and pi are reserved keywords for the imaginary unit, the base of the natural logarithm, ∞ and π, respectively.

Examples: 0, -1, 0.234, i, e, pi

See functions related to Arithmetic, Number operations, Trigonometry and Number theory.

boolean

Booleans represent either truth or falsity. The logical operations and, or and xor operate on and return booleans.

Examples: true, false

See functions related to Logic and Control flow.

string

Use strings to create non-mathematical text. Either ' or " can be used to delimit strings.

You can escape a character by placing a single backslash character before it. The following escape codes have special behaviour:

\n New-line
\{ \{
\} \}

If you want to write a string which contains a mixture of single and double quotes, you can delimit it with triple-double-quotes or triple-single-quotes, to save escaping too many characters.

Examples: "hello there", 'hello there', """ I said, "I'm Mike's friend" """

See functions related to Strings.

list

An ordered list of elements of any data type.

Examples: [0,1,2,3], [a,b,c], [true,false,true]

See functions related to Lists.

dict

A ‘dictionary’, mapping key strings to values of any data type.

A dictionary is created by enclosing one or more key-value pairs (a string followed by a colon and any JME expression) in square brackets, or with the dict function.

Key strings are case-sensitive.

Examples:

  • ["a": 1, "b": 2]
  • ["name": "Tess Tuser", "age": 106, "hobbies": ["reading","writing","arithmetic"] ]
  • dict("key1": 0.1, "key2": 1..3)
  • dict([["key1",1], ["key2",2]])

Warning

Because lists and dicts use similar syntax, [] produces an empty list, not an empty dictionary. To create an empty dictionary, use dict().

See functions related to Dictionaries and JSON.

range

A range a..b#c represents (roughly) the set of numbers \(\{a+nc \: | \: 0 \leq n \leq \frac{b-a}{c} \}\). If the step size is zero, then the range is the continuous interval \([a,b]\).

Examples: 1..3, 1..3#0.1, 1..3#0

See functions related to Ranges.

set

An unordered set of elements of any data type. The elements are pairwise distinct - if you create a set from a list with duplicate elements, the resulting set will not contain the duplicates.

Examples: set(a,b,c), set([1,2,3,4]), set(1..5)

See functions related to Sets.

vector

The components of a vector must be numbers.

When combining vectors of different dimensions, the smaller vector is padded with zeros to make up the difference.

Examples: vector(1,2), vector([1,2,3,4])

See functions related to Vector and matrix arithmetic.

matrix

Matrices are constructed from lists of numbers, representing the rows.

When combining matrices of different dimensions, the smaller matrix is padded with zeros to make up the difference.

Examples: matrix([1,2,3],[4,5,6]), matrix(row1,row2,row3)

See functions related to Vector and matrix arithmetic.

function

An application of a function.

Examples: f(x), sin(x)

op

An infix binary operation, or a pre-/post-fix unary operation.

Examples: x+y, n!, a and b

html

An HTML DOM node.

Examples: html("<div>things</div>")

See functions related to HTML.

expression

A JME sub-expression. Sub-expressions can be simplified, rearranged, pattern-matched, or evaluated using given values for their free variables.

See functions related to Sub-expressions.

Function reference

Arithmetic

x+y

Addition. Numbers, vectors, matrices, lists, dicts, or strings can be added together.

  • list1+list2 concatenates the two lists, while list+value returns a list with the right-hand-side value appended.
  • dict1+dict2 merges the two dictionaries, with values from the right-hand side taking precedence when the same key is present in both dictionaries.
Examples:
  • 1+23
  • vector(1,2)+vector(3,4)vector(4,6)
  • matrix([1,2],[3,4])+matrix([5,6],[7,8])matrix([6,8],[10,12])
  • [1,2,3]+4[1,2,3,4]
  • [1,2,3]+[4,5,6][1,2,3,4,5,6]
  • "hi "+"there""hi there"
x-y

Subtraction. Defined for numbers, vectors and matrices.

Examples:
  • 1-2-1
  • vector(3,2)-vector(1,4)vector(2,-2)
  • matrix([5,6],[3,4])-matrix([1,2],[7,8])matrix([4,4],[-4,-4])
x*y

Multiplication. Numbers, vectors and matrices can be multiplied together.

Examples:
  • 1*22
  • 2*vector(1,2,3)vector(2,4,6)
  • matrix([1,2],[3,4])*2matrix([2,4],[6,8])
  • matrix([1,2],[3,4])*vector(1,2)vector(5,11)
x/y

Division. Only defined for numbers.

Example:
  • 3/40.75.
x^y

Exponentiation. Only defined for numbers.

exp(x,y) is a synoynm for x^y.

Examples:
  • 3^29
  • exp(3,2)9
  • e^(pi * i)-1

Number operations

abs(x)
len(x)
length(x)

Absolute value, or modulus. Defined for numbers, strings, ranges, vectors, lists and dictionaries. In the case of a list, returns the number of elements. For a range, returns the difference between the upper and lower bounds. For a dictionary, returns the number of keys.

Examples:
  • abs(-8)8
  • abs(3-4i)5
  • abs("Hello")5
  • abs([1,2,3])3
  • len([1,2,3])3
  • len(set([1,2,2]))2
  • length(vector(3,4))5
  • abs(vector(3,4,12))13
  • len(["a": 1, "b": 2, "c": 1])3
arg(z)

Argument of a complex number.

Example:
  • arg(-1)pi
re(z)

Real part of a complex number.

Example:
  • re(1+2i)1
im(z)

Imaginary part of a complex number.

Example:
  • im(1+2i)2
conj(z)

Complex conjugate.

Example:
  • conj(1+i)1-i
isint(x)

Returns true if x is an integer.

Example:
  • isint(4.0)true
sqrt(x)
sqr(x)

Square root of a number.

Examples:
  • sqrt(4)2
  • sqrt(-1)i
root(x, n)

nth root of x.

Example:
  • root(8,3)2.
ln(x)

Natural logarithm.

Example:
  • ln(e)1
log(x)

Logarithm with base 10.

Example:
  • log(100)2.
log(x, b)

Logarithm with base b.

Example:
  • log(8,2)3.
degrees(x)

Convert radians to degrees.

Example:
  • degrees(pi/2)90
radians(x)

Convert degrees to radians.

Example:
  • radians(180)pi
sign(x)
sgn(x)

Sign of a number. Equivalent to \(\frac{x}{|x|}\), or 0 when x is 0.

Examples:
  • sign(3)1
  • sign(-3)-1
max(a, b)

Greatest of two numbers.

Example:
  • max(46,2)46
max(list)

Greatest of a list of numbers.

Example:
  • max([1,2,3])3
min(a, b)

Least of two numbers.

Example:
  • min(3,2)2
min(list)

Least of a list of numbers.

Example:
  • min([1,2,3])1
precround(n, d)

Round n to d decimal places. On matrices and vectors, this rounds each element independently.

Examples:
  • precround(pi,5)3.14159
  • precround(matrix([[0.123,4.56],[54,98.765]]),2)matrix([[0.12,4.56],[54,98.77]])
  • precround(vector(1/3,2/3),1)vector(0.3,0.7)
siground(n, f)

Round n to f significant figures. On matrices and vectors, this rounds each element independently.

Examples:
  • siground(pi,3)3.14
  • siground(matrix([[0.123,4.56],[54,98.765]]),2)matrix([[0.12,4.6],[54,99]])
  • siground(vector(10/3,20/3),2)vector(3.3,6.7)
withintolerance(a, b, t)

Returns true if \(b-t \leq a \leq b+t\).

Example:
  • withintolerance(pi,22/7,0.1)true
dpformat(n, d[, style])

Round n to d decimal places and return a string, padding with zeros if necessary.

If style is given, the number is rendered using the given notation style. See the page on Number notation for more on notation styles.

Example:
  • dpformat(1.2,4)"1.2000"
countdp(str)

Assuming str is a string representing a number, return the number of decimal places used. The string is passed through cleannumber() first.

Example:
  • countdp("1.0")1
  • countdp("1")0
  • countdp("not a number")0
sigformat(n, d[, style])

Round n to d significant figures and return a string, padding with zeros if necessary.

Example:
  • sigformat(4,3)"4.00"
countsigfigs(str)

Assuming str is a string representing a number, return the number of significant figures. The string is passed through cleannumber() first.

Example:
  • countsigfigs("1")1
  • countsigfigs("100")1
  • countsigfigs("1.0")2
  • countsigfigs("not a number")0
togivenprecision(str, precisionType, precision, strict)

Returns true if str is a string representing a number given to the desired number of decimal places or significant figures.

precisionType is either "dp", for decimal places, or "sigfig", for significant figures.

If strict is true, then trailing zeroes must be included.

Examples:
  • togivenprecision("1","dp",1,true)false
  • togivenprecision("1","dp",1,false)true
  • togivenprecision("1.0","dp",1,true)true
  • togivenprecision("100","sigfig",1,true)true
  • togivenprecision("100","sigfig",3,true)true
formatnumber(n, style)

Render the number n using the given number notation style.

See the page on Number notation for more on notation styles.

Example:
  • formatnumber(1234.567,"fr")"1.234,567"
cleannumber(str, styles)

Clean a string potentially representing a number. Remove space, and then try to identify a notation style, and rewrite to the plain-en style.

styles is a list of notation styles. If styles is given, str will be tested against the given styles. If it matches, the string will be rewritten using the matched integer and decimal parts, with punctuation removed and the decimal point changed to a dot.

Example:
  • cleannumber("100 000,02",["si-fr"])"100000.02"
  • cleannumber(" 1 ")"1"
  • cleannumber("1.0")"1.0"
string(n)

Render the number n using the plain-en notation style.

parsenumber(string, style)

Parse a string representing a number written in the given style.

If a list of styles is given, the first that accepts the given string is used.

See the page on Number notation for more on notation styles.

Examples:
  • parsenumber("1 234,567","si-fr")1234.567
  • parsenumber("1.001",["si-fr","eu"])1001
parsenumber_or_fraction(string, style)

Works the same as parsenumber(), but also accepts strings of the form number/number, which it interprets as fractions.

Example:
  • parsenumber_or_fraction("1/2")0.5
isnan(n)

Is n the “not a number” value, NaN?

Examples:
  • isnan(1)false
  • isnan(parsenumber("a","en"))true

Trigonometry

Trigonometric functions all work in radians, and have as their domain the complex numbers.

sin(x)

Sine.

cos(x)

Cosine.

tan(x)

Tangent: \(\tan(x) = \frac{\sin(x)}{\cos(x)}\)

cosec(x)

Cosecant: \(\csc(x) = \frac{1}{sin(x)}\)

sec(x)

Secant: \(\sec(x) = \frac{1}{cos(x)}\)

cot(x)

Cotangent: \(\cot(x) = \frac{1}{\tan(x)}\)

arcsin(x)

Inverse of sin(). When \(x \in [-1,1]\), arcsin(x) returns a value in \([-\frac{\pi}{2}, \frac{\pi}{2}]\).

arccos(x)

Inverse of cos(). When \(x \in [-1,1]\), arccos(x) returns a value in \([0, \frac{\pi}]\).

arctan(x)

Inverse of tan(). When \(x\) is non-complex, arctan(x) returns a value in \([-\frac{\pi}{2}, \frac{\pi}{2}]\).

sinh(x)

Hyperbolic sine: \(\sinh(x) = \frac{1}{2} \left( \mathrm{e}^x - \mathrm{e}^{-x} \right)\)

cosh(x)

Hyperbolic cosine: \(\cosh(x) = \frac{1}{2} \left( \mathrm{e}^x + \mathrm{e}^{-x} \right)\)

tanh(x)

Hyperbolic tangent: \(\tanh(x) = \frac{\sinh(x)}{\cosh(x)}\)

cosech(x)

Hyperbolic cosecant: \(\operatorname{cosech}(x) = \frac{1}{\sinh(x)}\)

sech(x)

Hyperbolic secant: \(\operatorname{sech}(x) = \frac{1}{\cosh(x)}\)

coth(x)

Hyperbolic cotangent: \(\coth(x) = \frac{1}{\tanh(x)}\)

arcsinh(x)

Inverse of sinh().

arccosh(x)

Inverse of cosh().

arctanh(x)

Inverse of tanh().

Number theory

x!

Factorial. When x is not an integer, \(\Gamma(x+1)\) is used instead.

fact(x) is a synoynm for x!.

Examples:
  • fact(3)6
  • 3!6
  • fact(5.5)287.885277815
factorise(n)

Factorise n. Returns the exponents of the prime factorisation of n as a list.

Examples
  • factorise(18)[1,2]
  • factorise(70)[1,0,1,1]
gamma(x)

Gamma function.

Examples:
  • gamma(3)2
  • gamma(1+i)0.4980156681 - 0.1549498283i
ceil(x)

Round up to the nearest integer. When x is complex, each component is rounded separately.

Examples:
  • ceil(3.2)4
  • ceil(-1.3+5.4i)-1+6i
floor(x)

Round down to the nearest integer. When x is complex, each component is rounded separately.

Example:
  • floor(3.5)3
round(x)

Round to the nearest integer. 0.5 is rounded up.

Examples:
  • round(0.1)0
  • round(0.9)1
  • round(4.5)5
  • round(-0.5)0
trunc(x)

If x is positive, round down to the nearest integer; if it is negative, round up to the nearest integer.

Example:
  • trunc(3.3)3
  • trunc(-3.3)-3
fract(x)

Fractional part of a number. Equivalent to x-trunc(x).

Example:
  • fract(4.3)0.3
rational_approximation(n[, accuracy])

Compute a rational approximation to the given number by computing terms of its continued fraction, returning the numerator and denominator separately. The approximation will be within \(e^{-\text{accuracy}}\) of the true value; the default value for accuracy is 15.

Examples:
  • rational_approximation(pi)[355,113]
  • rational_approximation(pi,3)[22,7]
mod(a, b)

Modulo; remainder after integral division, i.e. \(a \bmod b\).

Example:
  • mod(5,3)2
perm(n, k)

Count permutations, i.e. \(^n \kern-2pt P_k = \frac{n!}{(n-k)!}\).

Example:
  • perm(5,2)20
comb(n, k)

Count combinations, i.e. \(^n \kern-2pt C_k = \frac{n!}{k!(n-k)!}\).

Example:
  • comb(5,2)10.
gcd(a, b)
gcf(a, b)

Greatest common divisor of integers a and b. Can also write gcf(a,b).

Example:
  • gcd(12,16)4
gcd_without_pi_or_i(a, b)

Take out factors of \(\pi\) or \(i\) from a and b before computing their greatest common denominator.

Example:
  • gcd_without_pi_or_i(6*pi, 9)3
coprime(a, b)

Are a and b coprime? True if their gcd() is \(1\), or if either of a or b is not an integer.

Examples:
  • coprime(12,16)false
  • coprime(2,3)true
  • coprime(1,3)true
  • coprime(1,1)true
lcm(a, b)

Lowest common multiple of integers a and b. Can be used with any number of arguments; it returns the lowest common multiple of all the arguments.

Examples
  • lcm(8,12)24
  • lcm(8,12,5)120
x|y

x divides y.

Example:
  • 4|8true

Vector and matrix arithmetic

vector(a1, a2, ..., aN)

Create a vector with given components. Alternately, you can create a vector from a single list of numbers.

Examples:
  • vector(1,2,3)
  • vector([1,2,3])
matrix(row1, row2, ..., rowN)

Create a matrix with given rows, which should be lists of numbers. Or, you can pass in a single list of lists of numbers.

Examples:
  • matrix([1,2],[3,4])
  • matrix([[1,2],[3,4]])
id(n)

Identity matrix with \(n\) rows and columns.

Example:
  • id(3)matrix([[1,0,0],[0,1,0],[0,0,1])
numrows(matrix)

The number of rows in the given matrix

Example:
  • numrows(matrix([1,2],[3,4],[5,6])3
numcolumns(matrix)

The number of columns in the given matrix

Example:
  • numrows(matrix([1,2],[3,4],[5,6])2
rowvector(a1, a2, ..., aN)

Create a row vector (\(1 \times n\) matrix) with the given components. Alternately, you can create a row vector from a single list of numbers.

Examples:
  • rowvector(1,2)matrix([1,2])
  • rowvector([1,2])matrix([1,2])
dot(x, y)

Dot (scalar) product. Inputs can be vectors or column matrices.

Examples:
  • dot(vector(1,2,3),vector(4,5,6))32
  • dot(matrix([1],[2]), matrix([3],[4]))11
cross(x, y)

Cross product. Inputs can be vectors or column matrices.

Examples:
  • cross(vector(1,2,3),vector(4,5,6))vector(-3,6,-3)
  • cross(matrix([1],[2],[3]), matrix([4],[5],[6]))vector(-3,6,-3)
angle(a, b)

Angle between vectors a and b, in radians. Returns 0 if either a or b has length 0.

Example:
  • angle(vector(1,0),vector(0,1))pi/2
is_zero(x)

Returns true if every component of the vector x is zero.

Example:
  • is_zero(vector(0,0,0))true
det(x)

Determinant of a matrix. Throws an error if used on anything larger than a 3×3 matrix.

Examples:
  • det(matrix([1,2],[3,4]))-2
  • det(matrix([1,2,3],[4,5,6],[7,8,9]))0
transpose(x)

Matrix transpose. Can also take a vector, in which case it returns a single-row matrix.

Examples:
  • transpose(matrix([1,2],[3,4]))matrix([1,3],[2,4])
  • transpose(vector(1,2,3))matrix([1,2,3])
sum_cells(m)

Calculate the sum of all the cells in a matrix.

Example:
  • sum_cells(matrix([1,2],[3,4]))12

Strings

x[n]

Get the Nth character of the string x. Indices start at 0.

Example:
  • "hello"[1]"e"
x[a..b]

Slice the string x - get the substring between the given indices. Note that indices start at 0, and the final index is not included.

Example:
  • "hello"[1..4]"ell"
substring in string

Test if substring occurs anywhere in string. This is case-sensitive.

Example:
  • "plain" in "explains"true
latex(x)

Mark string x as containing raw LaTeX, so when it’s included in a mathmode environment it doesn’t get wrapped in a \textrm environment.

Note that backslashes must be double up, because the backslash is an escape character in JME strings.

Example:
  • latex('\\frac{1}{2}').
safe(x)

Mark string x as safe: don’t substitute variable values into it when this expression is evaluated.

Use this function to preserve curly braces in string literals.

Example:
  • safe('From { to }')
capitalise(x)

Capitalise the first letter of a string.

Example:
  • capitalise('hello there').
pluralise(n, singular, plural)

Return singular if n is 1, otherwise return plural.

Example:
  • pluralise(num_things,"thing","things")
upper(x)

Convert string to upper-case.

Example:
  • upper('Hello there').
lower(x)

Convert string to lower-case.

Example:
  • lower('CLAUS, Santa').
join(strings, delimiter)

Join a list of strings with the given delimiter.

Example:
  • join(['a','b','c'],',')'a,b,c'
split(string, delimiter)

Split a string at every occurrence of delimiter, returning a list of the the remaining pieces.

Example:
  • split("a,b,c,d",",")["a","b","c","d"]
trim(str)

Remove whitespace from the start and end of str.

Example:
  • trim(" a string  ")"a string"
currency(n, prefix, suffix)

Write a currency amount, with the given prefix or suffix characters.

Example:
  • currency(123.321,"£","")'£123.32'
separateThousands(n, separator)

Write a number, with the given separator character between every 3 digits

To write a number using notation appropriate to a particular culture or context, see formatnumber().

Example:
  • separateThousands(1234567.1234,",")'1,234,567.1234'
unpercent(str)

Get rid of the % on the end of a percentage and parse as a number, then divide by 100.

Example:
  • unpercent("2%")0.02
lpad(str, n, prefix)

Add copies of prefix to the start of str until the result is at least n characters long.

Example:
  • lpad("3", 2, "0")"03"
rpad(str, n, suffix)

Add copies of suffix to the end of str until the result is at least n characters long.

Example:
  • rpad("3", 2, "0")"30"
formatstring(str, values)

For each occurrence of %s in str, replace it with the corresponding entry in the list values.

Example:
  • formatstring("Their name is %s",["Hortense"])"Their name is Hortense"
  • formatstring("You should %s the %s",["simplify","denominator"])You should simplify the denominator"
letterordinal(n)

Get the \(n\)th element of the sequence a, b, c, ..., aa, ab, ....

Note that the numbering starts from 0.

Examples:
  • letterordinal(0)"a"
  • letterordinal(1)"b"
  • letterordinal(26)"aa"
match_regex(pattern, str, flags)

If str matches the regular expression pattern, returns a list of matched groups, otherwise returns an empty list.

This function uses JavaScript regular expression syntax.

flags is an optional string listing the options flags to use.

Examples:
  • match_regex("\\d+","01234")["01234"]
  • match_regex("a(b+)","abbbb")["abbbb","bbbb"]
  • match_regex("a(b+)","ABBBB")[]
  • match_regex("a(b+)","ABBBB","i")["ABBBB","BBBB"]
translate(str, arguments)

Translate the given string, if it’s in the localisation file.

Look at the default localisation file for strings which can be translated. This function takes a key representing a string to be translated, and returns the corresponding value from the current localisation file.

arguments is a dictionary of named substitutions to make in the string.

Examples:
  • translate("question.header",["number": 2])"Question 2" (when the en-GB locale is in use)
  • translate("question.header",["number": 2])"Pregunta 2" (when the es-ES locale is in use)
isbool(str)

After converting to lower case, is str any of the strings "true", "false", "yes" or "no"?

Examples:
  • isbool("true")true
  • isbool("YES")true
  • isbool("no")true
  • isbool("y")false

Logic

x<y

Returns true if x is less than y. Defined only for numbers.

Example:
  • 4<5
x>y

Returns true if x is greater than y. Defined only for numbers.

Example:
  • 5>4
x<=y

Returns true if x is less than or equal to y. Defined only for numbers.

Example:
  • 4<=4
x>=y

Returns true if x is greater than or equal to y. Defined only for numbers.

Example:
  • 4>=4
x<>y

Returns true if x is not equal to y. Defined for any data type. Returns true if x and y are not of the same data type.

Examples:
  • 'this string' <> 'that string'
  • 1<>2
  • '1' <> 1
x=y

Returns true if x is equal to y. Defined for any data type. Returns false if x and y are not of the same data type.

Examples:
  • vector(1,2)=vector(1,2,0)
  • 4.0=4
resultsequal(a, b, checkingFunction, accuracy)

Returns true if a and b are both of the same data type, and “close enough” according to the given checking function.

Vectors, matrices, and lists are considered equal only if every pair of corresponding elements in a and b is “close enough”.

checkingFunction is the name of a checking function to use. These are documented in the Numbas runtime documentation.

Examples:
  • resultsequal(22/7,pi,"absdiff",0.001)false
  • resultsequal(22/7,pi,"reldiff",0.001)true
x and y

Logical AND. Returns true if both x and y are true, otherwise returns false.

Examples:
  • true and true
  • true && true
  • true & true
not x

Logical NOT.

Examples:
  • not true
  • !true
x or y

Logical OR. Returns true when at least one of x and y is true. Returns false when both x and y are false.

Examples:
  • true or false
  • true || false
x xor y

Logical XOR. Returns true when at either x or y is true but not both. Returns false when x and y are the same expression.

Example:
  • true XOR false.
x implies y

Logical implication. If x is true and y is false, then the implication is false. Otherwise, the implication is true.

Example:
  • false implies true.

Ranges

a..b

Define a range. Includes all integers between and including a and b.

Examples:
  • 1..5
  • -6..6
a..b#s

Set the step size for a range. Default is 1. When s is 0, the range includes all real numbers between the limits.

Examples:
  • 0..1 # 0.1
  • 2..10 # 2
  • 0..1#0
a except b

Exclude a number, range, or list of items from a list or range.

Examples:
  • -9..9 except 0
  • -9..9 except [-1,1]
  • 3..8 except 4..6
  • [1,2,3,4,5] except [2,3]
list(range)

Convert a range to a list of its elements.

Example:
  • list(-2..2)[-2,-1,0,1,2]

Lists

x[n]

Get the nth element of list, vector or matrix x. For matrices, the nth row is returned.

Examples:
  • [0,1,2,3][1]1
  • vector(0,1,2)[2]2
  • matrix([0,1,2],[3,4,5],[6,7,8])[0]matrix([0,1,2])
x[a..b]
x[a..b#c]

Slice list x - return elements with indices in the given range. Note that list indices start at 0, and the final index is not included.

Example:
  • [0,1,2,3,4,5][1..3][1,2]
  • [0,1,2,3,4,5][1..6#2][1,3,5]
x in collection

Is element x in the list, set or range collection?

If collection is a dictionary, returns true if the dictionary has a key x.

Examples:
  • 3 in [1,2,3,4]true
  • 3 in (set(1,2,3,4) and set(2,4,6,8))false
  • "a" in ["a": 1]true
  • 1 in ["a": 1] throws an error because dictionary keys must be strings.
repeat(expression, n)

Evaluate expression n times, and return the results in a list.

Example:
  • repeat(random(1..4),5)[2, 4, 1, 3, 4]
all(list)

Returns true if every element of list is true.

Examples:
  • all([true,true])true
  • all([true,false])false
  • all([])true
some(list)

Returns true if at least one element of list is true.

Examples:
  • some([false,true,false])true
  • some([false,false,false])false
  • some([])false
map(expression,name[s],d)

Evaluate expression for each item in list, range, vector or matrix d, replacing variable name with the element from d each time.

You can also give a list of names if each element of d is a list of values. The Nth element of the list will be mapped to the Nth name.

Note

Do not use i or e as the variable name to map over - they’re already defined as mathematical constants!

Examples:
  • map(x+1,x,1..3)[2,3,4]
  • map(capitalise(s),s,["jim","bob"])["Jim","Bob"]
  • map(sqrt(x^2+y^2),[x,y],[ [3,4], [5,12] ])[5,13]
  • map(x+1,x,id(2))matrix([[2,1],[1,2]])
  • map(sqrt(x),x,vector(1,4,9))vector(1,2,3)
filter(expression, name, d)

Filter each item in list or range d, replacing variable name with the element from d each time, returning only the elements for which expression evaluates to true.

Note

Do not use i or e as the variable name to map over - they’re already defined as mathematical constants!

Example:
  • filter(x>5,x,[1,3,5,7,9])[7,9]
take(n, expression, name, d)

Take the first n elements from list or range d, replacing variable name with the element from d each time, returning only the elements for which expression evaluates to true.

This operation is lazy - once n elements satisfying the expression have been found, execution stops. You can use this to filter a few elements from a large list, where the condition might take a long time to calculate.

Note

Do not use i or e as the variable name to map over - they’re already defined as mathematical constants!

Example:
  • take(3,gcd(x,6)=1,x,10..30)[11,13,17]
let(name, definition, ..., expression)
let(definitions, expression)

Evaluate expression, temporarily defining variables with the given names. Use this to cut down on repetition. You can define any number of variables - in the first calling pattern, follow a variable name with its definition. Or you can give a dictionary mapping variable names to their values. The last argument is the expression to be evaluated.

Examples:
  • let(d,sqrt(b^2-4*a*ac), [(-b+d)/2, (-b-d)/2])[-2,-3] (when [a,b,c] = [1,5,6])
  • let(x,1, y,2, x+y)3
  • let(["x": 1, "y": 2], x+y)3
sort(x)

Sort list x.

Example:
  • sort([4,2,1,3])[1,2,3,4]
sort_destinations(x)

Return a list giving the index that each entry in the list will occupy after sorting.

Example:
  • sort_destinations([4,2,1,3])[3,1,0,2]
  • sort_destinations([1,2,3,4])[0,1,2,3]
reverse(x)

Reverse list x.

Example:
  • reverse([1,2,3])[3,2,1]
indices(list, value)

Find the indices at which value occurs in list.

Examples:
  • indices([1,0,1,0],1)[0,2]
  • indices([2,4,6],4)[1]
  • indices([1,2,3],5)[]
distinct(x)

Return a copy of the list x with duplicates removed.

Example:
  • distinct([1,2,3,1,4,3])[1,2,3,4]
list(x)

Convert set, vector or matrix x to a list of components (or rows, for a matrix).

Examples:
  • list(set(1,2,3))[1,2,3] (note that you can’t depend on the elements of sets being in any order)
  • list(vector(1,2))[1,2]
  • list(matrix([1,2],[3,4]))[[1,2], [3,4]]
satisfy(names, definitions, conditions, maxRuns)

Each variable name in names should have a corresponding definition expression in definitions. conditions is a list of expressions which you want to evaluate to true. The definitions will be evaluated repeatedly until all the conditions are satisfied, or the number of attempts is greater than maxRuns. If maxRuns isn’t given, it defaults to 100 attempts.

Example:
  • satisfy([a,b,c],[random(1..10),random(1..10),random(1..10)],[b^2-4*a*c>0])
sum(numbers)

Add up a list of numbers

Example:
  • sum([1,2,3])6
product(list1, list2, ..., listN) or product(list, n)

Cartesian product of lists. In other words, every possible combination of choices of one value from each given list.

If one list and a number are given, then the n-th Cartesian power of the list is returned: the Cartesian product of n copies of the list.

Example:
  • product([1,2],[a,b])[ [1,a], [1,b], [2,a], [2,b] ]
  • product([1,2],2)[ [1,1], [1,2], [2,1], [2,2] ]
zip(list1, list2, ..., listN)

Combine two (or more) lists into one - the Nth element of the output is a list containing the Nth elements of each of the input lists.

Example:
  • zip([1,2,3],[4,5,6])[ [1,4], [2,5], [3,6] ]
combinations(collection, r)

All ordered choices of r elements from collection, without replacement.

Example:
  • combinations([1,2,3],2)[ [1,2], [1,3], [2,3] ]
combinations_with_replacement(collection, r)

All ordered choices of r elements from collection, with replacement.

Example:
  • combinations([1,2,3],2)[ [1,1], [1,2], [1,3], [2,2], [2,3], [3,3] ]
permutations(collection, r)

All choices of r elements from collection, in any order, without replacement.

Example:
  • permutations([1,2,3],2)[ [1,2], [1,3], [2,1], [2,3], [3,1], [3,2] ]

Dictionaries

dict[key]

Get the value corresponding to the given key string in the dictionary d.

If the key is not present in the dictionary, an error will be thrown.

Example:
  • ["a": 1, "b": 2]["a"]1
get(dict, key, default)

Get the value corresponding to the given key string in the dictionary.

If the key is not present in the dictionary, the default value will be returned.

Examples:
  • get(["a":1], "a", 0)1
  • get(["a":1], "b", 0)0
dict(a:b, c:d, ...)
dict(pairs)

Create a dictionary with the given key-value pairs. Equivalent to [ .. ], except when no key-value pairs are given: [] creates an empty list instead.

You can alternately pass a list of pairs of the form [key, value], to transform a list into a dictionary.

Examples:
  • dict()
  • dict("a": 1, "b": 2)
  • dict([ ["a",1], ["b",2] ])
keys(dict)

A list of all of the given dictionary’s keys.

Example:
  • keys(["a": 1, "b": 2, "c": 1])["a","b","c"]
values(dict)
values(dict, keys)

A list of the values corresponding to each of the given dictionary’s keys.

If a list of keys is given, the values corresponding to those keys are returned, in the same order.

Examples:
  • values(["a": 1, "b": 2, "c": 1])[1,2,1]
  • values(["a": 1, "b": 2, "c": 3], ["b","a"])[2,1]
items(dict)

A list of all of the [key,value] pairs in the given dictionary.

Example:
  • values(["a": 1, "b": 2, "c": 1])[ ["a",1], ["b",2], ["c",1] ]

Sets

set(a,b,c,...) or set([elements])

Create a set with the given elements. Either pass the elements as individual arguments, or as a list.

Examples:
  • set(1,2,3)
  • set([1,2,3])
union(a, b)

Union of sets a and b

Examples:
  • union(set(1,2,3),set(2,4,6))set(1,2,3,4,6)
  • set(1,2,3) or set(2,4,6)set(1,2,3,4,6)
intersection(a, b)

Intersection of sets a and b, i.e. elements which are in both sets.

Examples:
  • intersection(set(1,2,3),set(2,4,6))set(2)
  • set(1,2,3) and set(2,4,6)set(2)
a-b

Set minus - elements which are in a but not b

Example:
  • set(1,2,3,4) - set(2,4,6)set(1,3)

Randomisation

random(x)

Pick uniformly at random from a range, list, or from the given arguments.

Examples:
  • random(1..5)
  • random([1,2,4])
  • random(1,2,3)
deal(n)

Get a random shuffling of the integers \([0 \dots n-1]\)

Example:
  • deal(3)[2,0,1]
shuffle(x) or shuffle(a..b)

Random shuffling of list or range.

Examples:
  • shuffle(["a","b","c"])["c","b","a"]
  • shuffle(0..4)[2,3,0,4,1]

Control flow

award(a, b)

Return a if b is true, else return 0.

Example:
  • award(5,true)5
if(p, a, b)

If p is true, return a, else return b. Only the returned value is evaluated.

Example:
  • if(false,1,0)0
switch(p1, a1, p2, a2, ..., pn, an, d)

Select cases. Alternating boolean expressions with values to return, with the final argument representing the default case. Only the returned value is evaluated.

Examples:
  • switch(true,1,false,0,3)1
  • switch(false,1,true,0,3)0
  • switch(false,1,false,0,3)3
assert(bool, value)

If bool is false, then return value, otherwise don’t evaluate value and return false. This is intended for use in marking scripts, to apply marking feedback only if a condition is met.

Example:
  • assert(studentAnswer<=0, correct("Student answer is positive"))
try(expression, name, except)

Try to evaluate expression. If it is successfully evaluated, return the result. Otherwise, evaluate except, with the error message available as name.

Examples:
  • try(eval(expression("x+")),err, "Error: "+err)"Error: Not enough arguments for operation <code>+</code>"
  • try(1+2,err,0)3

HTML

html(x)

Parse string x as HTML.

Example:
  • html('<div>Text!</div>')
isnonemptyhtml(str)

Does str represent a string of HTML containing text? Returns false for the empty string, or HTML elements with no text content.

Examples:
  • isnonemptyhtml("<p>Yes</p>")true
  • isnonemptyhtml("<p></p>")false
table(data), table(data, headers)

Create an HTML with cell contents defined by data, which should be a list of lists of data, and column headers defined by the list of strings headers.

Examples:
  • table([[0,1],[1,0]], ["Column A","Column B"])
  • table([[0,1],[1,0]])
image(url)

Create an HTML img element loading the image from the given URL. Images uploaded through the resources tab are stored in the relative URL resources/images/<filename>.png, where <filename> is the name of the original file.

Examples:

JSON

JSON is a lightweight data-interchange format. Many public data sets come in JSON format; it’s a good way of encoding data in a way that is easy for both humans and computers to read and write.

For an example of how you can use JSON data in a Numbas question, see the exam Working with JSON data.

json_decode(json)

Decode a JSON string into JME data types.

JSON is decoded into numbers, strings, booleans, lists, or dictionaries. To produce other data types, such as matrices or vectors, you will have to post-process the resulting data.

Warning

The JSON value null is silently converted to an empty string, because JME has no “null” data type. This may change in the future.

Example:
  • json_decode(' {"a": 1, "b": [2,true,"thing"]} ')["a": 1, "b": [2,true,"thing"]]
json_encode(data)

Convert the given object to a JSON string.

Numbers, strings, booleans, lists, and dictionaries are converted in a straightforward manner. Other data types may behave unexpectedly.

Example:
  • json_encode([1,"a",true])'[1,"a",true]'

Sub-expressions

expression(string)

Parse a string as a JME expression. The expression can be substituted into other expressions, such as the answer to a mathematical expression part, or the \simplify LaTeX command.

parse(string) is a synonym for expression(string).

Example:
eval(expression, values)

Evaluate the given sub-expression.

If values is given, it should be a dictionary mapping names of variables to their values.

Example:
  • eval(expression("1+2"))3
  • eval(expression("x+1"), ["x":1])2
args(expression)

Returns the arguments of the top-level operation of expression, as a list of sub-expressions. If expression is a data type other than an operation or function, an empty list is returned.

Binary operations only ever have two arguments. For example, 1+2+3 is parsed as (1+2)+3.

Examples:
  • args(expression("f(x)"))[expression("x")]
  • args(expression("1+2+3"))[expression("1+2"), expression("3")]
  • args(expression("1"))[]
type(expression)

Returns the name of the data type of the top token in the expression, as a string.

Examples:
  • type(x)"name"
  • type(1)"number"
  • type(x+1)"op"
  • type(sin(x))"function"
name(string)

Construct a name token with the given name.

Example:
  • name("x")x
string(name)

Return the given variable name as a string.

Example:
  • string(x)"x"
op(name)

Construct an operator with the given name.

Example:
  • op("+")+
exec(op, arguments)

Returns a sub-expression representing the application of the given operation to the list of arguments.

Example:
  • exec(op("+"), [2,1])expression("2+1")
  • exec(op("-"), [2,name("x")])expression("2-x")
findvars(expression)

Return a list of all unbound variables used in the given expression. Effectively, this is all the variables that need to be given values in order for this expression to be evaluated.

Bound variables are those defined as part of operations which also assign values to those variables, such as map or let.

Examples:
  • findvars(expression("x+1"))[x]
  • findvars(expression("x + x*y"))[x,y]
  • findvars(expression("map(x+2, x, [1,2,3])"))[]
simplify(expression, rules)

Apply the given simplification rules to expression, until no rules apply.

rules is a list of names of rules to apply, given either as a string containing a comma-separated list of names, or a list of strings.

Unlike the \simplify` command in content areas, the basic rule is not turned on by default.

See Substituting variables into displayed maths for a list of rules available.

Examples:
  • simplify(expression("1*x+cos(pi)","unitfactor"))expression("x+cos(pi)")
  • simplify(expression("1*x+cos(pi)"),["basic","unitfactor","trig"])expression("x-1")
canonical_compare(expr1, expr2)

Compare expressions a and b using the “canonical” ordering. Returns -1 if a should go before b, 0 if they are considered “equal”, and 1 if a should go after b.

Expressions are examined in the following order:

  • Names used: all variable names used in each expression are collected in a depth-first search and the resulting lists are compared lexicographically.
  • Data type: if a and b are of different data types, op and function go first, and then they are compared using the names of their data types.
  • Polynomials: terms of the form x^b or a*x^b, where a and b are numbers and x is a variable name, go before anything else.
  • Function name: if a and b are both function applications, they are compared using the names of the functions. If the functions are the same, the arguments are compared. Powers, or multiples of powers, go after anything else.
  • Number: if a and b are both numbers, the lowest number goes first. Complex numbers are compared by real part and then by imaginary part.
  • Elements of other data types are considered to be equal to any other value of the same data type.
Examples:
  • canonical_compare(a,b)-1
  • canonical_compare(f(y),g(x))1
  • canonical_compare(f(x),g(x))-1
  • canonical_compare("a","b")0

Pattern-matching sub-expressions

match(expr, pattern)

If expr matches pattern, return a dictionary of the form ["match": boolean, "groups": dict], where "groups" is a dictionary mapping names of matches to sub-expressions.

The match is non-commutative, so for example x*y is not considered to be the same as y*x. You can use m_commute() to allow matching up to rearrangement of arguments.

See pattern-matching for more on matching mathematical expressions.

If you don’t need to use any parts of the matched expression, use matches() instead.

Examples:
  • match(expression("x+1"),"?;a + ?;b")["match": true, "groups": ["a": expression("x"), "b": expression("1")])
  • match(expression("sin(x)", "?;a + ?;b")["match": false, "groups": []]
  • match(expression("x+1"),"1+?;a")["match": false, "groups": []]
  • match(expression("x+1"),"m_commute(1+?;a)")["match": true, "groups": ["a": expression("x")]]
matches(expr, pattern)

Return true if expr matches pattern.

Use this if you’re not interested in capturing any parts of the matched expression.

Examples:
  • matches(expression("x+1"),"?;a + ?;b")true
  • match(expression("sin(x)", "?;a + ?;b")false
replace(pattern, replacement, expr)

Replace occurrences of pattern in expr with the expression created by substituting the matched items into replacement.

Examples:
  • replace("?;x + ?;y", "x*y", expression("1+2"))expression("1*2")
  • replace("?;x + ?;y", "f(x,y)", expression("1+2+3"))expression("f(f(1,2),3)")
  • replace("0*?", "0", expression("0*sin(x) + x*0 + 2*cos(0*pi)"))expression("0 + x*0 + 2*cos(0)")

Identifying data types

type(x)

Returns the name of the data type of x.

Example:
  • type(1)"number"
x isa type

Returns true if x is of the data type type.

Examples:
  • 1 isa "number"true
  • x isa "name"true (if x is not defined in this scope)
  • x isa "number"true (if x has a numerical value in this scope)

Inspecting the evaluation scope

definedvariables()

Returns a list containing the names of every variable defined in the current scope, as strings.

isset(name)

Returns true if the variable with the given name has been defined in the current scope.

unset(items, expression)

Delete the named variables, functions and rulesets before evaluating the given expression.

items is a dictionary with keys "variables", "functions" and "rulesets", which are each lists of names to delete.