LINALG

diff - diff computes differences of arrays.

Status

Experimental

Class

Pure function.

Description

y = diff(x) returns differences between adjacent elements of vector x.
y = diff(x, n) returns the nth difference by applying the diff(x) operator recursively n times.
B = diff(A) returns differences between adjacent elements of array A along the first dimension.
B = diff(A, n) returns the nth difference by applying the diff(A) operator recursively n times.
B = diff(A, dim) returns differences between adjacent elements of array A along the dimension given by dim.
B = diff(A, n, dim) returns the nth difference along the dimension given by dim by applying the diff(A, dim) operator recursively n times.

Syntax

For vector:
result = diff(x [, n])

For matrix:
result = diff(A [, n, dim])

Arguments

x: Shall be a real type of verctor. A: Shall be a real type of matrix.

n (optional): Shall be a integer type. dim (optional): Shall be a integer type.

Return value

Return differences between adjacent elements of vector x or matrix A.

Example

program test_linalg_diff
    use forlab_linalg, only: diff
    use forlab_linalg, only: linspace
    use forlab_io, only: disp

    real :: x(10)

    call linspace(x, 0.0, 9.0)
    call disp(x, "linspace(x) : ")
    call disp(diff(x), "test_linalg_diff : ")


end program test_linalg_diff

zeros/ones

Description

zeros creates a rank-1 or rank-2 array of the given shape, filled completely with 0 integer type values.
ones creates a rank-1 or rank-2 array of the given shape, filled completely with 1 integer type values.

Warning

It is not recommended to use the zeros/ones function, it is recommended to use allocate(array(dim1, dim2, ..), source=0.0/1.0).

Status

Experimental

Class

Pure function.

Syntax

For rank-1 array:
result = zeros(dim)
result = ones(dim)

For rank-2 array:
result = zeros(dim1, dim2)
result = ones(dim1, dim2)

Arguments

dim/dim1: Shall be an integer type. This is an intent(in) argument.

dim2: Shall be an integer type. This is an intent(in) argument.

Return value

Returns a rank-1 or rank-2 array of the given shape, filled completely with either 0 or 1 integer type values.

Warning

Since the result of ones is of integer type, one should be careful about using it in arithmetic expressions. For example:

real :: A(:,:)
!> Be careful
A = ones(2,2)/2     !! A = 1/2 = 0.0
!> Recommend
A = ones(2,2)/2.0   !! A = 1/2.0 = 0.5

Example

program demo_linalg_zerosones
    use forlab_linalg, only: zeros, ones
    use forlab_io, only: disp

    real, allocatable :: zero(:, :), one(:, :)
    real, allocatable :: array(:, :)

    zero = zeros(1, 2)
    one  = ones (2, 1)

    call disp(zero, "zeros: ")
    call disp(one , "ones : ")

    call disp(ones(2, 2)/2, "!attention: `ones(2, 2)/2` is like `1/2 == 0`")

    array = zeros(2, 2)
    call disp(array, "array with zeros: ")

    array = ones (2, 2)
    call disp(array, "array with ones :")

end program demo_linalg_zerosones