.. currentmodule:: Base
*********
Numbers
*********
Standard Numeric Types
----------------------
``Bool`` ``Int8`` ``UInt8`` ``Int16`` ``UInt16`` ``Int32`` ``UInt32`` ``Int64`` ``UInt64`` ``Int128`` ``UInt128`` ``Float16`` ``Float32`` ``Float64`` ``Complex64`` ``Complex128``
Data Formats
------------
.. function:: bin(n, [pad])
.. Docstring generated from Julia source
Convert an integer to a binary string, optionally specifying a number of digits to pad to.
.. function:: hex(n, [pad])
.. Docstring generated from Julia source
Convert an integer to a hexadecimal string, optionally specifying a number of digits to pad to.
.. function:: dec(n, [pad])
.. Docstring generated from Julia source
Convert an integer to a decimal string, optionally specifying a number of digits to pad to.
.. function:: oct(n, [pad])
.. Docstring generated from Julia source
Convert an integer to an octal string, optionally specifying a number of digits to pad to.
.. function:: base(base, n, [pad])
.. Docstring generated from Julia source
Convert an integer to a string in the given base, optionally specifying a number of digits to pad to.
.. function:: digits([T], n, [base], [pad])
.. Docstring generated from Julia source
Returns an array with element type ``T`` (default ``Int``\ ) of the digits of ``n`` in the given base, optionally padded with zeros to a specified size. More significant digits are at higher indexes, such that ``n == sum([digits[k]*base^(k-1) for k=1:length(digits)])``\ .
.. function:: digits!(array, n, [base])
.. Docstring generated from Julia source
Fills an array of the digits of ``n`` in the given base. More significant digits are at higher indexes. If the array length is insufficient, the least significant digits are filled up to the array length. If the array length is excessive, the excess portion is filled with zeros.
.. function:: bits(n)
.. Docstring generated from Julia source
A string giving the literal bit representation of a number.
.. function:: parse(type, str, [base])
.. Docstring generated from Julia source
Parse a string as a number. If the type is an integer type, then a base can be specified (the default is 10). If the type is a floating point type, the string is parsed as a decimal floating point number. If the string does not contain a valid number, an error is raised.
.. function:: tryparse(type, str, [base])
.. Docstring generated from Julia source
Like ``parse``\ , but returns a ``Nullable`` of the requested type. The result will be null if the string does not contain a valid number.
.. function:: big(x)
.. Docstring generated from Julia source
Convert a number to a maximum precision representation (typically ``BigInt`` or ``BigFloat``\ ). See ``BigFloat`` for information about some pitfalls with floating-point numbers.
.. function:: signed(x)
.. Docstring generated from Julia source
Convert a number to a signed integer. If the argument is unsigned, it is reinterpreted as signed without checking for overflow.
.. function:: unsigned(x) -> Unsigned
.. Docstring generated from Julia source
Convert a number to an unsigned integer. If the argument is signed, it is reinterpreted as unsigned without checking for negative values.
.. function:: float(x)
.. Docstring generated from Julia source
Convert a number, array, or string to a ``AbstractFloat`` data type. For numeric data, the smallest suitable ``AbstractFloat`` type is used. Converts strings to ``Float64``\ .
.. function:: significand(x)
.. Docstring generated from Julia source
Extract the ``significand(s)`` (a.k.a. mantissa), in binary representation, of a floating-point number or array. If ``x`` is a non-zero finite number, then the result will be a number of the same type on the interval :math:`[1,2)`\ . Otherwise ``x`` is returned.
.. doctest::
julia> significand(15.2)/15.2
0.125
julia> significand(15.2)*8
15.2
.. function:: exponent(x) -> Int
.. Docstring generated from Julia source
Get the exponent of a normalized floating-point number.
.. function:: complex(r, [i])
.. Docstring generated from Julia source
Convert real numbers or arrays to complex. ``i`` defaults to zero.
.. function:: bswap(n)
.. Docstring generated from Julia source
Byte-swap an integer.
.. function:: num2hex(f)
.. Docstring generated from Julia source
Get a hexadecimal string of the binary representation of a floating point number.
.. function:: hex2num(str)
.. Docstring generated from Julia source
Convert a hexadecimal string to the floating point number it represents.
.. function:: hex2bytes(s::AbstractString)
.. Docstring generated from Julia source
Convert an arbitrarily long hexadecimal string to its binary representation. Returns an ``Array{UInt8,1}``\ , i.e. an array of bytes.
.. function:: bytes2hex(bin_arr::Array{UInt8, 1})
.. Docstring generated from Julia source
Convert an array of bytes to its hexadecimal representation. All characters are in lower-case. Returns a ``String``\ .
General Number Functions and Constants
--------------------------------------
.. function:: one(x)
.. Docstring generated from Julia source
Get the multiplicative identity element for the type of ``x`` (``x`` can also specify the type itself). For matrices, returns an identity matrix of the appropriate size and type.
.. function:: zero(x)
.. Docstring generated from Julia source
Get the additive identity element for the type of ``x`` (``x`` can also specify the type itself).
.. data:: pi
π
.. Docstring generated from Julia source
The constant pi.
.. data:: im
.. Docstring generated from Julia source
The imaginary unit.
.. data:: e
eu
.. Docstring generated from Julia source
The constant e.
.. data:: catalan
.. Docstring generated from Julia source
Catalan's constant.
.. data:: γ
eulergamma
.. Docstring generated from Julia source
Euler's constant.
.. data:: φ
golden
.. Docstring generated from Julia source
The golden ratio.
.. data:: Inf
.. Docstring generated from Julia source
Positive infinity of type ``Float64``\ .
.. data:: Inf32
.. Docstring generated from Julia source
Positive infinity of type ``Float32``\ .
.. data:: Inf16
.. Docstring generated from Julia source
Positive infinity of type ``Float16``\ .
.. data:: NaN
.. Docstring generated from Julia source
A not-a-number value of type ``Float64``\ .
.. data:: NaN32
.. Docstring generated from Julia source
A not-a-number value of type ``Float32``\ .
.. data:: NaN16
.. Docstring generated from Julia source
A not-a-number value of type ``Float16``\ .
.. function:: issubnormal(f) -> Bool
.. Docstring generated from Julia source
Test whether a floating point number is subnormal.
.. function:: isfinite(f) -> Bool
.. Docstring generated from Julia source
Test whether a number is finite
.. function:: isinf(f) -> Bool
.. Docstring generated from Julia source
Test whether a number is infinite.
.. function:: isnan(f) -> Bool
.. Docstring generated from Julia source
Test whether a floating point number is not a number (NaN).
.. function:: nextfloat(x::AbstractFloat)
.. Docstring generated from Julia source
Returns the smallest floating point number ``y`` of the same type as ``x`` such ``x < y``\ . If no such ``y`` exists (e.g. if ``x`` is ``Inf`` or ``NaN``\ ), then returns ``x``\ .
.. function:: prevfloat(x::AbstractFloat)
.. Docstring generated from Julia source
Returns the largest floating point number ``y`` of the same type as ``x`` such ``y < x``\ . If no such ``y`` exists (e.g. if ``x`` is ``-Inf`` or ``NaN``\ ), then returns ``x``\ .
.. function:: nextfloat(x::AbstractFloat, n::Integer)
.. Docstring generated from Julia source
The result of ``n`` iterative applications of ``nextfloat`` to ``x`` if ``n >= 0``\ , or ``-n`` applications of ``prevfloat`` if ``n < 0``\ .
.. function:: isinteger(x) -> Bool
.. Docstring generated from Julia source
Test whether ``x`` or all its elements are numerically equal to some integer
.. function:: isreal(x) -> Bool
.. Docstring generated from Julia source
Test whether ``x`` or all its elements are numerically equal to some real number.
.. function:: isimag(z) -> Bool
.. Docstring generated from Julia source
Test whether ``z`` is purely imaginary, i.e. has a real part equal to 0.
.. function:: Float32(x [, mode::RoundingMode])
.. Docstring generated from Julia source
Create a Float32 from ``x``\ . If ``x`` is not exactly representable then ``mode`` determines how ``x`` is rounded.
.. doctest::
julia> Float32(1/3, RoundDown)
0.3333333f0
julia> Float32(1/3, RoundUp)
0.33333334f0
See :obj:`RoundingMode` for available rounding modes.
.. function:: Float64(x [, mode::RoundingMode])
.. Docstring generated from Julia source
Create a Float64 from ``x``\ . If ``x`` is not exactly representable then ``mode`` determines how ``x`` is rounded.
.. doctest::
julia> Float64(pi, RoundDown)
3.141592653589793
julia> Float64(pi, RoundUp)
3.1415926535897936
See :obj:`RoundingMode` for available rounding modes.
.. function:: BigInt(x)
.. Docstring generated from Julia source
Create an arbitrary precision integer. ``x`` may be an ``Int`` (or anything that can be converted to an ``Int``\ ). The usual mathematical operators are defined for this type, and results are promoted to a ``BigInt``\ .
Instances can be constructed from strings via :func:`parse`\ , or using the ``big`` string literal.
.. function:: BigFloat(x)
.. Docstring generated from Julia source
Create an arbitrary precision floating point number. ``x`` may be an ``Integer``\ , a ``Float64`` or a ``BigInt``\ . The usual mathematical operators are defined for this type, and results are promoted to a ``BigFloat``\ .
Note that because decimal literals are converted to floating point numbers when parsed, ``BigFloat(2.1)`` may not yield what you expect. You may instead prefer to initialize constants from strings via :func:`parse`\ , or using the ``big`` string literal.
.. doctest::
julia> BigFloat(2.1)
2.100000000000000088817841970012523233890533447265625000000000000000000000000000
julia> big"2.1"
2.099999999999999999999999999999999999999999999999999999999999999999999999999986
.. function:: rounding(T)
.. Docstring generated from Julia source
Get the current floating point rounding mode for type ``T``\ , controlling the rounding of basic arithmetic functions (:func:`+`\ , :func:`-`\ , :func:`*`\ , :func:`/` and :func:`sqrt`\ ) and type conversion.
See :obj:`RoundingMode` for available modes.
.. function:: setrounding(T, mode)
.. Docstring generated from Julia source
Set the rounding mode of floating point type ``T``\ , controlling the rounding of basic arithmetic functions (:func:`+`\ , :func:`-`\ , :func:`*`\ , :func:`/` and :func:`sqrt`\ ) and type conversion. Other numerical functions may give incorrect or invalid values when using rounding modes other than the default ``RoundNearest``\ .
Note that this may affect other types, for instance changing the rounding mode of ``Float64`` will change the rounding mode of ``Float32``\ . See :obj:`RoundingMode` for available modes.
.. warning::
This feature is still experimental, and may give unexpected or incorrect values.
.. function:: setrounding(f::Function, T, mode)
.. Docstring generated from Julia source
Change the rounding mode of floating point type ``T`` for the duration of ``f``\ . It is logically equivalent to:
.. code-block:: julia
old = rounding(T)
setrounding(T, mode)
f()
setrounding(T, old)
See :obj:`RoundingMode` for available rounding modes.
.. warning::
This feature is still experimental, and may give unexpected or incorrect values. A known problem is the interaction with compiler optimisations, e.g.
.. code-block:: julia
julia> setrounding(Float64,RoundDown) do
1.1 + 0.1
end
1.2000000000000002
Here the compiler is *constant folding*, that is evaluating a known constant expression at compile time, however the rounding mode is only changed at runtime, so this is not reflected in the function result. This can be avoided by moving constants outside the expression, e.g.
.. code-block:: julia
julia> x = 1.1; y = 0.1;
julia> setrounding(Float64,RoundDown) do
x + y
end
1.2
.. function:: get_zero_subnormals() -> Bool
.. Docstring generated from Julia source
Returns ``false`` if operations on subnormal floating-point values ("denormals") obey rules for IEEE arithmetic, and ``true`` if they might be converted to zeros.
.. function:: set_zero_subnormals(yes::Bool) -> Bool
.. Docstring generated from Julia source
If ``yes`` is ``false``\ , subsequent floating-point operations follow rules for IEEE arithmetic on subnormal values ("denormals"). Otherwise, floating-point operations are permitted (but not required) to convert subnormal inputs or outputs to zero. Returns ``true`` unless ``yes==true`` but the hardware does not support zeroing of subnormal numbers.
``set_zero_subnormals(true)`` can speed up some computations on some hardware. However, it can break identities such as ``(x-y==0) == (x==y)``\ .
Integers
~~~~~~~~
.. function:: count_ones(x::Integer) -> Integer
.. Docstring generated from Julia source
Number of ones in the binary representation of ``x``\ .
.. doctest::
julia> count_ones(7)
3
.. function:: count_zeros(x::Integer) -> Integer
.. Docstring generated from Julia source
Number of zeros in the binary representation of ``x``\ .
.. doctest::
julia> count_zeros(Int32(2 ^ 16 - 1))
16
.. function:: leading_zeros(x::Integer) -> Integer
.. Docstring generated from Julia source
Number of zeros leading the binary representation of ``x``\ .
.. doctest::
julia> leading_zeros(Int32(1))
31
.. function:: leading_ones(x::Integer) -> Integer
.. Docstring generated from Julia source
Number of ones leading the binary representation of ``x``\ .
.. doctest::
julia> leading_ones(UInt32(2 ^ 32 - 2))
31
.. function:: trailing_zeros(x::Integer) -> Integer
.. Docstring generated from Julia source
Number of zeros trailing the binary representation of ``x``\ .
.. doctest::
julia> trailing_zeros(2)
1
.. function:: trailing_ones(x::Integer) -> Integer
.. Docstring generated from Julia source
Number of ones trailing the binary representation of ``x``\ .
.. doctest::
julia> trailing_ones(3)
2
.. function:: isodd(x::Integer) -> Bool
.. Docstring generated from Julia source
Returns ``true`` if ``x`` is odd (that is, not divisible by 2), and ``false`` otherwise.
.. doctest::
julia> isodd(9)
true
julia> isodd(10)
false
.. function:: iseven(x::Integer) -> Bool
.. Docstring generated from Julia source
Returns ``true`` is ``x`` is even (that is, divisible by 2), and ``false`` otherwise.
.. doctest::
julia> iseven(9)
false
julia> iseven(10)
true
BigFloats
---------
The ``BigFloat`` type implements arbitrary-precision floating-point arithmetic using the `GNU MPFR library `_.
.. function:: precision(num::AbstractFloat)
.. Docstring generated from Julia source
Get the precision of a floating point number, as defined by the effective number of bits in the mantissa.
.. function:: precision(BigFloat)
.. Docstring generated from Julia source
Get the precision (in bits) currently used for ``BigFloat`` arithmetic.
.. function:: setprecision([T=BigFloat,] precision::Int)
.. Docstring generated from Julia source
Set the precision (in bits) to be used for ``T`` arithmetic.
.. function:: setprecision(f::Function, [T=BigFloat,] precision::Integer)
.. Docstring generated from Julia source
Change the ``T`` arithmetic precision (in bits) for the duration of ``f``\ . It is logically equivalent to:
.. code-block:: julia
old = precision(BigFloat)
setprecision(BigFloat, precision)
f()
setprecision(BigFloat, old)
Often used as ``setprecision(T, precision) do ... end``
.. _random-numbers:
Random Numbers
--------------
Random number generation in Julia uses the `Mersenne Twister library `_ via ``MersenneTwister`` objects.
Julia has a global RNG, which is used by default. Other RNG types can be plugged in by inheriting the ``AbstractRNG`` type;
they can then be used to have multiple streams of random numbers.
Besides ``MersenneTwister``, Julia also provides the ``RandomDevice`` RNG type, which is a wrapper over the OS provided entropy.
Most functions related to random generation accept an optional ``AbstractRNG`` as the first argument, ``rng`` , which defaults to the global one if not provided.
Morever, some of them accept optionally dimension specifications ``dims...`` (which can be given as a tuple) to generate arrays of random values.
A ``MersenneTwister`` or ``RandomDevice`` RNG can generate random numbers of the following types:
``Float16``, ``Float32``, ``Float64``, ``Bool``, ``Int8``, ``UInt8``, ``Int16``, ``UInt16``,
``Int32``, ``UInt32``, ``Int64``, ``UInt64``, ``Int128``, ``UInt128``, ``BigInt``
(or complex numbers of those types). Random floating point numbers are generated uniformly in :math:`[0, 1)`.
As ``BigInt`` represents unbounded integers, the interval must be specified (e.g. ``rand(big(1:6))``).
.. function:: srand([rng], [seed])
.. Docstring generated from Julia source
Reseed the random number generator. If a ``seed`` is provided, the RNG will give a reproducible sequence of numbers, otherwise Julia will get entropy from the system. For ``MersenneTwister``\ , the ``seed`` may be a non-negative integer, a vector of ``UInt32`` integers or a filename, in which case the seed is read from a file. ``RandomDevice`` does not support seeding.
.. function:: MersenneTwister([seed])
.. Docstring generated from Julia source
Create a ``MersenneTwister`` RNG object. Different RNG objects can have their own seeds, which may be useful for generating different streams of random numbers.
.. function:: RandomDevice()
.. Docstring generated from Julia source
Create a ``RandomDevice`` RNG object. Two such objects will always generate different streams of random numbers.
.. function:: rand([rng], [S], [dims...])
.. Docstring generated from Julia source
Pick a random element or array of random elements from the set of values specified by ``S``\ ; ``S`` can be
* an indexable collection (for example ``1:n`` or ``['x','y','z']``\ ), or
* a type: the set of values to pick from is then equivalent to ``typemin(S):typemax(S)`` for integers (this is not applicable to ``BigInt``\ ), and to :math:`[0, 1)` for floating point numbers;
``S`` defaults to ``Float64``\ .
.. function:: rand!([rng], A, [coll])
.. Docstring generated from Julia source
Populate the array ``A`` with random values. If the indexable collection ``coll`` is specified, the values are picked randomly from ``coll``\ . This is equivalent to ``copy!(A, rand(rng, coll, size(A)))`` or ``copy!(A, rand(rng, eltype(A), size(A)))`` but without allocating a new array.
.. function:: bitrand([rng], [dims...])
.. Docstring generated from Julia source
Generate a ``BitArray`` of random boolean values.
.. function:: randn([rng], [T=Float64], [dims...])
.. Docstring generated from Julia source
Generate a normally-distributed random number of type ``T`` with mean 0 and standard deviation 1. Optionally generate an array of normally-distributed random numbers. The ``Base`` module currently provides an implementation for the types ``Float16``\ , ``Float32``\ , and ``Float64`` (the default).
.. function:: randn!([rng], A::AbstractArray) -> A
.. Docstring generated from Julia source
Fill the array ``A`` with normally-distributed (mean 0, standard deviation 1) random numbers. Also see the ``rand`` function.
.. function:: randexp([rng], [T=Float64], [dims...])
.. Docstring generated from Julia source
Generate a random number of type ``T`` according to the exponential distribution with scale 1. Optionally generate an array of such random numbers. The ``Base`` module currently provides an implementation for the types ``Float16``\ , ``Float32``\ , and ``Float64`` (the default).
.. function:: randexp!([rng], A::AbstractArray) -> A
.. Docstring generated from Julia source
Fill the array ``A`` with random numbers following the exponential distribution (with scale 1).
.. function:: randjump(r::MersenneTwister, jumps, [jumppoly]) -> Vector{MersenneTwister}
.. Docstring generated from Julia source
Create an array of the size ``jumps`` of initialized ``MersenneTwister`` RNG objects where the first RNG object given as a parameter and following ``MersenneTwister`` RNGs in the array initialized such that a state of the RNG object in the array would be moved forward (without generating numbers) from a previous RNG object array element on a particular number of steps encoded by the jump polynomial ``jumppoly``\ .
Default jump polynomial moves forward ``MersenneTwister`` RNG state by 10^20 steps.