Julia ships with predefined types representing both complex and rational numbers, and supports all standard mathematical operations on them. Conversion and Promotion are defined so that operations on any combination of predefined numeric types, whether primitive or composite, behave as expected.
The global constant im is bound to the complex number i, representing the principal square root of -1. It was deemed harmful to co-opt the name i for a global constant, since it is such a popular index variable name. Since Julia allows numeric literals to be juxtaposed with identifiers as coefficients, this binding suffices to provide convenient syntax for complex numbers, similar to the traditional mathematical notation:
julia> 1 + 2im
1 + 2im
You can perform all the standard arithmetic operations with complex numbers:
julia> (1 + 2im)*(2 - 3im)
8 + 1im
julia> (1 + 2im)/(1 - 2im)
-0.6 + 0.8im
julia> (1 + 2im) + (1 - 2im)
2 + 0im
julia> (-3 + 2im) - (5 - 1im)
-8 + 3im
julia> (-1 + 2im)^2
-3 - 4im
julia> (-1 + 2im)^2.5
2.729624464784009 - 6.9606644595719im
julia> (-1 + 2im)^(1 + 1im)
-0.27910381075826657 + 0.08708053414102428im
julia> 3(2 - 5im)
6 - 15im
julia> 3(2 - 5im)^2
-63 - 60im
julia> 3(2 - 5im)^-1.0
0.20689655172413793 + 0.5172413793103449im
The promotion mechanism ensures that combinations of operands of different types just work:
julia> 2(1 - 1im)
2 - 2im
julia> (2 + 3im) - 1
1 + 3im
julia> (1 + 2im) + 0.5
1.5 + 2.0im
julia> (2 + 3im) - 0.5im
2.0 + 2.5im
julia> 0.75(1 + 2im)
0.75 + 1.5im
julia> (2 + 3im) / 2
1.0 + 1.5im
julia> (1 - 3im) / (2 + 2im)
-0.5 - 1.0im
julia> 2im^2
-2 + 0im
julia> 1 + 3/4im
1.0 - 0.75im
Note that 3/4im == 3/(4*im) == -(3/4*im), since a literal coefficient binds more tightly than division.
Standard functions to manipulate complex values are provided:
julia> real(1 + 2im)
1
julia> imag(1 + 2im)
2
julia> conj(1 + 2im)
1 - 2im
julia> abs(1 + 2im)
2.23606797749979
julia> abs2(1 + 2im)
5
As is common, the absolute value of a complex number is its distance from zero. The abs2 function gives the square of the absolute value, and is of particular use for complex numbers, where it avoids taking a square root. The full gamut of other Elementary Functions is also defined for complex numbers:
julia> sqrt(im)
0.7071067811865476 + 0.7071067811865475im
julia> sqrt(1 + 2im)
1.272019649514069 + 0.7861513777574233im
julia> cos(1 + 2im)
2.0327230070196656 - 3.0518977991517997im
julia> exp(1 + 2im)
-1.1312043837568138 + 2.471726672004819im
julia> sinh(1 + 2im)
-0.48905625904129374 + 1.4031192506220407im
Note that mathematical functions typically return real values when applied to real numbers and complex values when applied to complex numbers. For example, sqrt, for example, behaves differently when applied to -1 versus -1 + 0im even though -1 == -1 + 0im:
julia> sqrt(-1)
ERROR: DomainError()
in sqrt at math.jl:111
julia> sqrt(-1 + 0im)
0.0 + 1.0im
The literal numeric coefficient notation does not work when constructing complex number from variables. Instead, the multiplication must be explicitly written out:
julia> a = 1; b = 2; a + b*im
1 + 2im
Hoever, this is not recommended; Use the complex function instead to construct a complex value directly from its real and imaginary parts.:
julia> complex(a,b)
1 + 2im
This construction avoids the multiplication and addition operations.
Inf and NaN propagate through complex numbers in the real and imaginary parts of a complex number as described in the Special floating-point values section:
julia> 1 + Inf*im
complex(1.0,Inf)
julia> 1 + NaN*im
complex(1.0,NaN)
Julia has a rational number type to represent exact ratios of integers. Rationals are constructed using the // operator:
julia> 2//3
2//3
If the numerator and denominator of a rational have common factors, they are reduced to lowest terms such that the denominator is non-negative:
julia> 6//9
2//3
julia> -4//8
-1//2
julia> 5//-15
-1//3
julia> -4//-12
1//3
This normalized form for a ratio of integers is unique, so equality of rational values can be tested by checking for equality of the numerator and denominator. The standardized numerator and denominator of a rational value can be extracted using the num and den functions:
julia> num(2//3)
2
julia> den(2//3)
3
Direct comparison of the numerator and denominator is generally not necessary, since the standard arithmetic and comparison operations are defined for rational values:
julia> 2//3 == 6//9
true
julia> 2//3 == 9//27
false
julia> 3//7 < 1//2
true
julia> 3//4 > 2//3
true
julia> 2//4 + 1//6
2//3
julia> 5//12 - 1//4
1//6
julia> 5//8 * 3//12
5//32
julia> 6//5 / 10//7
21//25
Rationals can be easily converted to floating-point numbers:
julia> float(3//4)
0.75
Conversion from rational to floating-point respects the following identity for any integral values of a and b, with the exception of the case a == 0 and b == 0:
julia> isequal(float(a//b), a/b)
true
Constructing infinite rational values is acceptable:
julia> 5//0
Inf
julia> -3//0
-Inf
julia> typeof(ans)
Rational{Int64}
Trying to construct a NaN rational value, however, is not:
julia> 0//0
invalid rational: 0//0
As usual, the promotion system makes interactions with other numeric types effortless:
julia> 3//5 + 1
8//5
julia> 3//5 - 0.5
0.1
julia> 2//7 * (1 + 2im)
2//7 + 4//7im
julia> 2//7 * (1.5 + 2im)
0.42857142857142855 + 0.5714285714285714im
julia> 3//2 / (1 + 2im)
3//10 - 3//5im
julia> 1//2 + 2im
1//2 + 2//1im
julia> 1 + 2//3im
1//1 + 2//3im
julia> 0.5 == 1//2
true
julia> 0.33 == 1//3
false
julia> 0.33 < 1//3
true
julia> 1//3 - 0.33
0.0033333333333332993