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Merged
merged 6 commits into from
Dec 8, 2021
Merged

stdlib_selection: correction of typos and addition of some checks #585

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1b6ae52
update stdlib_selection typo
jvdp1 Dec 1, 2021
64b1b0e
add checks
jvdp1 Dec 1, 2021
1822ccd
remove surplus conditions
jvdp1 Dec 2, 2021
0312d3d
change comment following @ivan-pi
jvdp1 Dec 3, 2021
b6f442c
change following @gareth-nx
jvdp1 Dec 3, 2021
cbc3262
add commment for module pr_selection
jvdp1 Dec 5, 2021
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5 changes: 3 additions & 2 deletions doc/specs/stdlib_selection.md
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@ which implements selection algorithms.
## Overview of the module

The module `stdlib_selection` defines two generic subroutines:

* `select` is used to find the k-th smallest entry of an array. The input
array is also modified in-place, and on return will be partially sorted
such that `all(array(1:k) <= array(k)))` and `all(array(k) <= array((k+1):size(array)))` is true.
Expand Down Expand Up @@ -159,7 +160,7 @@ Generic subroutine.

`array` : shall be a rank one array of any of the types:
`integer(int8)`, `integer(int16)`, `integer(int32)`, `integer(int64)`,
`real(sp)`, `real(dp)`, `real(xdp), `real(qp)`. It is an `intent(in)` argument. On input it is
`real(sp)`, `real(dp)`, `real(xdp)`, `real(qp)`. It is an `intent(in)` argument. On input it is
the array in which we search for the k-th smallest entry.

`indx`: shall be a rank one array with the same size as `array`, containing all integers
Expand Down Expand Up @@ -198,7 +199,7 @@ The code does not support `NaN` elements in `array`; it will run, but there is
no consistent interpretation given to the order of `NaN` entries of `array`
compared to other entries.

While it is essential that that `indx` contains a permutation of the integers `1:size(array)`,
While it is essential that `indx` contains a permutation of the integers `1:size(array)`,
the code does not check for this. For example if `size(array) == 4`, then we could have
`indx = [4, 2, 1, 3]` or `indx = [1, 2, 3, 4]`, but not `indx = [2, 1, 2, 4]`. It is the user's
responsibility to avoid such errors.
Expand Down
16 changes: 10 additions & 6 deletions src/stdlib_selection.fypp
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Expand Up @@ -4,6 +4,8 @@
! The index arrays are of all INT_KINDS_TYPES

module stdlib_selection
!! Quickly find the k-th smallest value of an array, or the index of the k-th smallest value.
!! ([Specification](../page/specs/stdlib_selection.html))
!
! This code was modified from the "Coretran" implementation "quickSelect" by
! Leon Foks, https://github.com/leonfoks/coretran/tree/master/src/sorting
Expand Down Expand Up @@ -85,9 +87,10 @@ contains
r = size(a, kind=ip)
if(present(right)) r = right

if(k < 1_ip .or. k > size(a, kind=ip) .or. l > r .or. l < 1_ip .or. &
r > size(a, kind=ip)) then
error stop "select must have 1 <= k <= size(a), and 1 <= left <= right <= size(a)";
if(l > r .or. l < 1_ip .or. r > size(a, kind=ip) &
.or. k < l .or. k > r & !i.e. if k is not in the interval [l; r]
) then
error stop "select must have 1 <= left <= k <= right <= size(a)";
end if

searchk: do
Expand Down Expand Up @@ -201,9 +204,10 @@ contains
error stop "arg_select must have size(a) == size(indx)"
end if

if(k < 1_ip .or. k > size(a, kind=ip) .or. l > r .or. l < 1_ip .or. &
r > size(a, kind=ip)) then
error stop "arg_select must have 1 <= k <= size(a), and 1 <= left <= right <= size(a)";
if(l > r .or. l < 1_ip .or. r > size(a, kind=ip) &
.or. k < l .or. k > r & !i.e. if k is not in the interval [l; r]
) then
error stop "arg_select must have 1 <= left <= k <= right <= size(a)";
end if

searchk: do
Expand Down