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Init of covariance
Squashed commit of the following: commit c7d6c1d Author: Vandenplas, Jeremie <jeremie.vandenplas@gmail.com> Date: Sun Apr 12 10:18:15 2020 +0200 covariance: addition of tests commit 9cd7e63 Author: Vandenplas, Jeremie <jeremie.vandenplas@gmail.com> Date: Sun Apr 12 00:12:41 2020 +0200 covariance:comment commit 958b59b Author: Vandenplas, Jeremie <jeremie.vandenplas@wur.nl> Date: Sat Apr 11 23:46:40 2020 +0200 covariance: correct test commit fdf4e54 Author: Vandenplas, Jeremie <jeremie.vandenplas@gmail.com> Date: Sat Apr 11 22:57:23 2020 +0200 covariance: update spec commit c3c277f Author: Vandenplas, Jeremie <jeremie.vandenplas@gmail.com> Date: Sat Apr 11 22:35:11 2020 +0200 covariance: support of cov for vectors commit c60ce03 Author: Vandenplas, Jeremie <jeremie.vandenplas@gmail.com> Date: Sat Apr 11 21:46:41 2020 +0200 covariance: real + complex+integer commit 9e3eba0 Author: Vandenplas, Jeremie <jeremie.vandenplas@gmail.com> Date: Fri Apr 10 23:16:48 2020 +0200 covariance: addition of complex commit 340309e Author: Vandenplas, Jeremie <jeremie.vandenplas@gmail.com> Date: Fri Apr 10 22:32:17 2020 +0200 covariance: init
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‎src/CMakeLists.txt

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@@ -5,6 +5,7 @@ set(fppFiles
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stdlib_experimental_io.fypp
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stdlib_experimental_optval.fypp
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stdlib_experimental_stats.fypp
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stdlib_experimental_stats_cov.fypp
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stdlib_experimental_stats_mean.fypp
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stdlib_experimental_stats_moment.fypp
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stdlib_experimental_stats_var.fypp

‎src/stdlib_experimental_stats.fypp

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@@ -8,7 +8,102 @@ module stdlib_experimental_stats
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implicit none
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private
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! Public API
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public :: mean, moment, var
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public :: cov, mean, moment, var
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interface cov
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#:for k1, t1 in RC_KINDS_TYPES
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#:set RName = rname("cov",1, t1, k1)
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module function ${RName}$(x, dim, mask, corrected) result(res)
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${t1}$, intent(in) :: x(:)
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integer, intent(in) :: dim
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logical, intent(in), optional :: mask
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logical, intent(in), optional :: corrected
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real(${k1}$) :: res
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end function ${RName}$
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#:endfor
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#:for k1, t1 in INT_KINDS_TYPES
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#:set RName = rname("cov",1, t1, k1, 'dp')
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module function ${RName}$(x, dim, mask, corrected) result(res)
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${t1}$, intent(in) :: x(:)
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integer, intent(in) :: dim
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logical, intent(in), optional :: mask
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logical, intent(in), optional :: corrected
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real(dp) :: res
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end function ${RName}$
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#:endfor
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#:for k1, t1 in RC_KINDS_TYPES
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#:set RName = rname("cov_mask",1, t1, k1)
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module function ${RName}$(x, dim, mask, corrected) result(res)
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${t1}$, intent(in) :: x(:)
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integer, intent(in) :: dim
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logical, intent(in) :: mask(:)
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logical, intent(in), optional :: corrected
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real(${k1}$) :: res
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end function ${RName}$
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#:endfor
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#:for k1, t1 in INT_KINDS_TYPES
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#:set RName = rname("cov_mask",1, t1, k1, 'dp')
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module function ${RName}$(x, dim, mask, corrected) result(res)
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${t1}$, intent(in) :: x(:)
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integer, intent(in) :: dim
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logical, intent(in) :: mask(:)
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logical, intent(in), optional :: corrected
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real(dp) :: res
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end function ${RName}$
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#:endfor
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#:for k1, t1 in RC_KINDS_TYPES
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#:set RName = rname("cov",2, t1, k1)
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module function ${RName}$(x, dim, mask, corrected) result(res)
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${t1}$, intent(in) :: x(:, :)
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integer, intent(in) :: dim
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logical, intent(in), optional :: mask
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logical, intent(in), optional :: corrected
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${t1}$ :: res(merge(size(x, 1), size(x, 2), mask = 1<dim)&
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, merge(size(x, 1), size(x, 2), mask = 1<dim))
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end function ${RName}$
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#:endfor
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#:for k1, t1 in INT_KINDS_TYPES
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#:set RName = rname("cov",2, t1, k1, 'dp')
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module function ${RName}$(x, dim, mask, corrected) result(res)
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${t1}$, intent(in) :: x(:, :)
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integer, intent(in) :: dim
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logical, intent(in), optional :: mask
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logical, intent(in), optional :: corrected
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real(dp) :: res(merge(size(x, 1), size(x, 2), mask = 1<dim)&
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, merge(size(x, 1), size(x, 2), mask = 1<dim))
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end function ${RName}$
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#:endfor
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#:for k1, t1 in RC_KINDS_TYPES
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#:set RName = rname("cov_mask",2, t1, k1)
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module function ${RName}$(x, dim, mask, corrected) result(res)
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${t1}$, intent(in) :: x(:, :)
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integer, intent(in) :: dim
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logical, intent(in) :: mask(:,:)
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logical, intent(in), optional :: corrected
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${t1}$ :: res(merge(size(x, 1), size(x, 2), mask = 1<dim)&
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, merge(size(x, 1), size(x, 2), mask = 1<dim))
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end function ${RName}$
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#:endfor
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#:for k1, t1 in INT_KINDS_TYPES
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#:set RName = rname("cov_mask",2, t1, k1, 'dp')
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module function ${RName}$(x, dim, mask, corrected) result(res)
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${t1}$, intent(in) :: x(:, :)
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integer, intent(in) :: dim
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logical, intent(in) :: mask(:,:)
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logical, intent(in), optional :: corrected
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real(dp) :: res(merge(size(x, 1), size(x, 2), mask = 1<dim)&
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, merge(size(x, 1), size(x, 2), mask = 1<dim))
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end function ${RName}$
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#:endfor
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end interface cov
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interface mean
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#:for k1, t1 in RC_KINDS_TYPES
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end interface var
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interface moment
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#:for k1, t1 in RC_KINDS_TYPES
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#:for rank in RANKS

‎src/stdlib_experimental_stats.md

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# Descriptive statistics
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* [`cov` - covariance of array elements](#cov---covariance-of-array-elements)
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* [`mean` - mean of array elements](#mean---mean-of-array-elements)
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* [`moment` - central moments of array elements](#moment---central-moments-of-array-elements)
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* [`var` - variance of array elements](#var---variance-of-array-elements)
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## `cov` - covariance of array elements
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### Description
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Returns the covariance of the elements of `array` along dimension `dim` if the corresponding element in `mask` is `true` (if `mask` is provided).
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Per default, the covariance is defined as:
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```
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cov(array) = 1/(n-1) sum_i (array(i) - mean(array) * (array(i) - mean(array)) )
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```
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where n is the number of elements.
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The scaling can be changed with the logical argument `corrected`. If `corrected` is `.false.`, then the sum is scaled with `n`, otherwise with `n-1`.
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### Syntax
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`result = cov(array, dim [, mask [, corrected]])`
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### Arguments
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`array`: Shall be a 1-rank or a 2-rank array of type `integer`, `real`, or `complex`.
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`dim`: Shall be a scalar of type `integer` with a value in the range from 1 to n, where n is the rank of `array`.
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`mask` (optional): Shall be of type `logical` and either by a scalar or an array of the same shape as `array`.
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`corrected` (optional): Shall be a scalar of type `logical`. If `corrected` is `.true.` (default value), the sum is scaled with `n-1`. If `corrected` is `.false.`, then the sum is scaled with `n`.
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### Return value
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If `array` is of rank 1 and of type `real` or `complex`, the result is of the same type `real` corresponding to the type of `array`.
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If `array` is of rank 2 and of type `real` or `complex`, the result is of the same type as `array`.
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If `array` is of type `integer`, the result is of type `real(dp)`.
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If `array` is of rank 1, a scalar with the covariance (that is the variance) of all elements in `array` is returned.
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If `array` is of rank 2, a 2-rank array is returned.
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If `mask` is specified, the result is the covariance of all elements of `array` corresponding to `true` elements of `mask`. If every element of `mask` is `false`, the result is IEEE `NaN`.
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### Example
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```fortran
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program demo_cov
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use stdlib_experimental_stats, only: cov
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implicit none
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real :: x(1:6) = [ 1., 2., 3., 4., 5., 6. ]
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real :: y(1:2, 1:3) = reshape([ 1., 2., 3., 4., 5., 6. ], [ 2, 3])
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print *, cov(x, 1) !returns 3.5
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print *, cov(x, 1, corrected = .false.) !returns 2.9167
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print *, cov(y, 1) !returns a square matrix of size 3 with all elements equal to 0.5
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end program demo_cov
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```
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## `mean` - mean of array elements
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### Description

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