Mathematical Operations¶

Arithmetic and Bitwise Operators¶

The following arithmetic operators are supported on all primitive numeric types:

• +x — unary plus is the identity operation.
• -x — unary minus maps values to their additive inverses.
• x + y — binary plus performs addition.
• x - y — binary minus performs subtraction.
• x * y — times performs multiplication.
• x / y — divide performs division.

The following bitwise operators are supported on all primitive integer types:

• ~x — bitwise not.
• x & y — bitwise and.
• x | y — bitwise or.
• x $ y — bitwise xor.
• x >>> y — logical shift right.
• x >> y — arithmetic shift right.
• x << y — logical/arithmetic shift left.

Here are some simple examples using arithmetic operators:

julia> 1 + 2 + 3
6

julia> 1 - 2
-1

julia> 3*2/12
0.5

(By convention, we tend to space less tightly binding operators less tightly, but there are no syntactic constraints.)

Julia’s promotion system makes arithmetic operations on mixtures of argument types “just work” naturally and automatically. See Conversion and Promotion for details of the promotion system.

Here are some examples with bitwise operators:

julia> ~123
-124

julia> 123 & 234
106

julia> 123 | 234
251

julia> 123 $ 234
145

julia> ~uint32(123)
0xffffff84

julia> ~uint8(123)
0x84

Every binary arithmetic and bitwise operator also has an updating version that assigns the result of the operation back into its left operand. For example, the updating form of + is the += operator. Writing x += 3 is equivalent to writing x = x + 3:

julia> x = 1
1

julia> x += 3
4

julia> x
4

The updating versions of all the binary arithmetic and bitwise operators are:

+=  -=  *=  /=  &=  |=  $=  >>>=  >>=  <<=

Numeric Comparisons¶

Standard comparison operations are defined for all the primitive numeric types:

• == — equality.
• != — inequality.
• < — less than.
• <= — less than or equal to.
• > — greater than.
• >= — greater than or equal to.

Here are some simple examples:

julia> 1 == 1
true

julia> 1 == 2
false

julia> 1 != 2
true

julia> 1 == 1.0
true

julia> 1 < 2
true

julia> 1.0 > 3
false

julia> 1 >= 1.0
true

julia> -1 <= 1
true

julia> -1 <= -1
true

julia> -1 <= -2
false

julia> 3 < -0.5
false

Integers are compared in the standard manner — by comparison of bits. Floating-point numbers are compared according to the IEEE 754 standard:

• finite numbers are ordered in the usual manner
• Inf is equal to itself and greater than everything else except NaN
• -Inf is equal to itself and less then everything else except NaN
• NaN is not equal to, less than, or greater than anything, including itself.

The last point is potentially suprprising and thus worth noting:

julia> NaN == NaN
false

julia> NaN != NaN
true

julia> NaN < NaN
false

julia> NaN > NaN
false

For situations where one wants to compare floating-point values so that NaN equals NaN, such as hash key comparisons, the function isequal is also provided, which considers NaNs to be equal to each other:

julia> isequal(NaN,NaN)
true

Mixed-type comparisons between signed integers, unsigned integers, and floats can be very tricky. A great deal of care has been taken to ensure that Julia does them correctly.

Unlike most languages, with the notable exception of Python, comparisons can be arbitrarily chained:

julia> 1 < 2 <= 2 < 3 == 3 > 2 >= 1 == 1 < 3 != 5
true

Chaining comparisons is often quite convenient in numerical code. Chained numeric comparisons use the & operator, which allows them to work on arrays. For example, 0 < A < 1 gives a boolean array whose entries are true where the corresponding elements of A are between 0 and 1.

Note the evaluation behavior of chained comparisons:

v(x) = (println(x); x)

julia> v(1) < v(2) <= v(3)
2
1
3
false

The middle expression is only evaluated once, rather than twice as it would be if the expression were written as v(1) > v(2) & v(2) <= v(3). However, the order of evaluations in a chained comparison is undefined. It is strongly recommended not to use expressions with side effects (such as printing) in chained comparisons. If side effects are required, the short-circuit && operator should be used explicitly (see Short-Circuit Evaluation).

Mathematical Functions¶

Julia provides a comprehensive collection of mathematical functions and operators. These mathematical operations are defined over as broad a class of numerical values as permit sensible definitions, including integers, floating-point numbers, rationals, and complexes, wherever such definitions make sense.

• round(x) — round x to the nearest integer.
• iround(x) — round x to the nearest integer, giving an integer-typed result.
• floor(x) — round x towards -Inf.
• ifloor(x) — round x towards -Inf, giving an integer-typed result.
• ceil(x) — round x towards +Inf.
• iceil(x) — round x towards +Inf, giving an integer-typed result.
• trunc(x) — round x towards zero.
• itrunc(x) — round x towards zero, giving an integer-typed result.
• div(x,y) — truncated division; quotient rounded towards zero.
• fld(x,y) — floored division; quotient rounded towards -Inf.
• rem(x,y) — remainder; satisfies x == div(x,y)*y + rem(x,y), implying that sign matches x.
• mod(x,y) — modulus; satisfies x == fld(x,y)*y + mod(x,y), implying that sign matches y.
• gcd(x,y...) — greatest common divisor of x, y... with sign matching x.
• lcm(x,y...) — least common multiple of x, y... with sign matching x.
• abs(x) — a positive value with the magnitude of x.
• abs2(x) — the squared magnitude of x.
• sign(x) — indicates the sign of x, returning -1, 0, or +1.
• signbit(x) — indicates whether the sign bit is on (1) or off (0).
• copysign(x,y) — a value with the magnitude of x and the sign of y.
• flipsign(x,y) — a value with the magnitude of x and the sign of x*y.
• sqrt(x) — the square root of x.
• cbrt(x) — the cube root of x.
• hypot(x,y) — accurate sqrt(x^2 + y^2) for all values of x and y.
• exp(x) — the natural exponential function at x.
• expm1(x) — accurate exp(x)-1 for x near zero.
• ldexp(x,n) — x*2^n computed efficiently for integer values of n.
• log(x) — the natural logarithm of x.
• log(b,x) — the base b logarithm of x.
• log2(x) — the base 2 logarithm of x.
• log10(x) — the base 10 logarithm of x.
• log1p(x) — accurate log(1+x) for x near zero.
• logb(x) — returns the binary exponent of x.
• erf(x) — the error function at x.
• erfc(x) — accurate 1-erf(x) for large x.
• gamma(x) — the gamma function at x.
• lgamma(x) — accurate log(gamma(x)) for large x.

For an overview of why functions like hypot, expm1, log1p, and erfc are necessary and useful, see John D. Cook’s excellent pair of blog posts on the subject: expm1, log1p, erfc, and hypot.

All the standard trigonometric functions are also defined:

sin    cos    tan    cot    sec    csc
sinh   cosh   tanh   coth   sech   csch
asin   acos   atan   acot   asec   acsc
acoth  asech  acsch  sinc   cosc   atan2

These are all single-argument functions, with the exception of atan2, which gives the angle in radians between the x-axis and the point specified by its arguments, interpreted as x and y coordinates. In order to compute trigonometric functions with degrees instead of radians, suffix the function with d. For example, sind(x) computes the sine of x where x is specified in degrees.

For notational convenience, the rem functions has an operator form:

• x % y is equivalent to rem(x,y).

The spelled-out rem operator is the “canonical” form, while the % operator form is retained for compatibility with other systems. Like arithmetic and bitwise operators, % and ^ also have updating forms. As with other updating forms, x %= y means x = x % y and x ^= y means x = x^y:

julia> x = 2; x ^= 5; x
32

julia> x = 7; x %= 4; x
3