A poor implement only for review.

Author: zoziha

CHANGELOG.md

@@ -22,6 +22,7 @@ Features available from the latest git source
   - new procedures `arg`, `argd` and `argpi`
     [#498](https://github.com/fortran-lang/stdlib/pull/498)
   - new procedure `diff`
+    [#605](https://github.com/fortran-lang/stdlib/pull/605)
 
 Changes to existing modules
 

src/stdlib_math.fypp

@@ -367,15 +367,17 @@ module stdlib_math
     interface diff
         #:set RI_KINDS_TYPES = REAL_KINDS_TYPES + INT_KINDS_TYPES
         #:for k1, t1 in RI_KINDS_TYPES
-        pure module function diff_1_${k1}$(x, n) result(Y)
+        pure module function diff_1_${k1}$(x, n, prepend, append) result(Y)
             ${t1}$, intent(in) :: x(:)
             integer, intent(in), optional :: n
+            ${t1}$, intent(in), optional :: prepend(:), append(:)
             ${t1}$, allocatable :: Y(:)
         end function diff_1_${k1}$
-        pure module function diff_2_${k1}$(X, n, dim) result(Y)
+        pure module function diff_2_${k1}$(X, n, dim, prepend, append) result(Y)
             ${t1}$, intent(in) :: X(:, :)
             integer, intent(in), optional :: n, dim
-            ${t1}$, allocatable :: Y(:,:)
+            ${t1}$, intent(in), optional :: prepend(:, :), append(:, :)
+            ${t1}$, allocatable :: Y(:, :)
         end function diff_2_${k1}$
         #:endfor
     end interface diff

src/stdlib_math_diff.fypp

@@ -12,27 +12,49 @@ contains
     #! `diff` computes differences of arrays of the ${t1}$ type.
 
     #:for k1, t1 in RI_KINDS_TYPES
-    pure module function diff_1_${k1}$(X, n) result(Y)
+    pure module function diff_1_${k1}$(X, n, prepend, append) result(Y)
         ${t1}$, intent(in) :: X(:)
         integer, intent(in), optional :: n
+        ${t1}$, intent(in), optional :: prepend(:), append(:)
         ${t1}$, allocatable :: Y(:)
+        integer :: size_prepend, size_append
         integer :: n_, i
 
+        size_prepend = 0
+        size_append = 0
         n_ = optval(n, 1)
+        if (present(prepend)) size_prepend = size(prepend) 
+        if (present(append)) size_append = size(append)
+        
+        if (size(X) + size_prepend + size_append <= n_) then
+            allocate(Y(0))
+            return
+        end if
 
-        Y = X
+        if (size_prepend > 0) then
+            Y = [prepend, X]
+        else
+            Y = X
+        end if
+        if (size_append > 0) Y = [Y, append]
+        
         do i = 1, n_
             Y = Y(2:) - Y(:size(Y) - 1)
         end do
 
     end function diff_1_${k1}$
 
-    pure module function diff_2_${k1}$(X, n, dim) result(Y)
+    pure module function diff_2_${k1}$(X, n, dim, prepend, append) result(Y)
         ${t1}$, intent(in) :: X(:, :)
         integer, intent(in), optional :: n, dim
+        ${t1}$, intent(in), optional :: prepend(:, :), append(:, :)
         ${t1}$, allocatable :: Y(:, :)
+        integer :: size_prepend, size_append
         integer :: n_, dim_, i
+        ${t1}$, allocatable :: tmp(:, :)
 
+        size_prepend = 0
+        size_append = 0
         n_ = optval(n, 1)
         if (present(dim)) then
             if (dim == 1 .or. dim == 2) then
@@ -44,15 +66,34 @@ contains
             dim_ = 1
         end if
 
-        Y = X
+        if (present(prepend)) size_prepend = size(prepend, dim_)
+        if (present(append)) size_append = size(append, dim_)
+        
+        if (size(X, dim_) + size_prepend + size_append <= n_) then
+            allocate(Y(0, 0))
+            return
+        end if
+        
         if (dim_ == 1) then
+            allocate(tmp(size(X, 1)+size_prepend+size_append, size(X, 2)))
+            if (size_prepend > 0) tmp(:size_prepend, :) = prepend
+            tmp(size_prepend+1:size(X, 1)+size_prepend, :) = X
+            if (size_append > 0) tmp(size(X, 1)+size_prepend+1:, :) = append
+            Y = tmp
             do i = 1, n_
                 Y = Y(2:, :) - Y(:size(Y, 1) - 1, :)
             end do
-        elseif (dim == 2) then
+
+        elseif (dim_ == 2) then
+            allocate(tmp(size(x, 1), size(X, 2)+size_prepend+size_append))
+            if (size_prepend > 0) tmp(:, :size_prepend) = prepend
+            tmp(:, size_prepend+1:size(X, 2)+size_prepend) = X
+            if (size_append > 0) tmp(:, size(X, 2)+size_prepend+1:) = append
+            Y = tmp
             do i = 1, n_
                 Y = Y(:, 2:) - Y(:, :size(Y, 2) - 1)
             end do
+            
         end if
 
     end function diff_2_${k1}$

src/tests/math/test_stdlib_math.fypp

@@ -378,6 +378,7 @@ contains
         type(error_type), allocatable, intent(out) :: error
         ${t1}$ :: x(6) = [${t1}$ :: 0, 5, 15, 30, 50, 75]
         ${t1}$ :: A(1, 3) = reshape([${t1}$ :: 1, 3, 5], [1, 3])
+        ${t1}$ :: B(2) = [${t1}$ :: 1, 2]
 
         call check(error, all_close(diff(x), [${t1}$ :: 5, 10, 15, 20, 25]), &
             "diff(x) in test_diff_real_${k1}$ failed")
@@ -387,10 +388,27 @@ contains
             "diff(x, n=2) in test_diff_real_${k1}$ failed")
         if (allocated(error)) return
 
+        call check(error, all_close(diff(x, prepend=[${t1}$ :: 1]), [${t1}$ :: -1, 5, 10, 15, 20, 25]), &
+            "diff(x, prepend=[${t1}$ :: 1]) in test_diff_real_${k1}$ failed")
+        if (allocated(error)) return
+        call check(error, all_close(diff(x, append=[${t1}$ :: 1]), [${t1}$ :: 5, 10, 15, 20, 25, -74]), &
+            "diff(x, append=[${t1}$ :: 1]) in test_diff_real_${k1}$ failed")
+        
         call check(error, all_close(diff(A, n=1, dim=2), reshape([${t1}$ :: 2, 2], [1, 2])), &
             "diff(x, n=1, dim=2) in test_diff_real_${k1}$ failed")
         if (allocated(error)) return
 
+        call check(error, all_close(diff(A, n=1, dim=2, prepend=reshape([${t1}$ :: 1], [1, 1]), &
+            append=reshape([${t1}$ :: 2], [1, 1])), reshape([${t1}$ :: 0, 2, 2, -3], [1, 4])), &
+            "diff(x, n=1, dim=2, prepend=reshape([${t1}$ :: 1], [1, 1]), &
+            &append=reshape([${t1}$ :: 2], [1, 1])) in test_diff_real_${k1}$ failed")
+        if (allocated(error)) return
+        
+        call check(error, size(diff(B, 2)), 0, "size(diff(B, 2)) in test_diff_real_${k1}$ failed")
+        if (allocated(error)) return
+        call check(error, size(diff(B, 3)), 0, "size(diff(B, 3)) in test_diff_real_${k1}$ failed")
+        if (allocated(error)) return
+        
     end subroutine test_diff_real_${k1}$
     #:endfor
 
@@ -399,6 +417,7 @@ contains
         type(error_type), allocatable, intent(out) :: error
         ${t1}$ :: x(6) = [${t1}$ :: 0, 5, 15, 30, 50, 75]
         ${t1}$ :: A(1, 3) = reshape([${t1}$ :: 1, 3, 5], [1, 3])
+        ${t1}$ :: B(2) = [${t1}$ :: 1, 2]
 
         call check(error, all(diff(x) == [${t1}$ :: 5, 10, 15, 20, 25]), &
             "diff(x) in test_diff_int_${k1}$ failed")
@@ -412,6 +431,10 @@ contains
             "diff(A, n=1, dim=2) in test_diff_int_${k1}$ failed")
         if (allocated(error)) return
 
+        call check(error, size(diff(B, 2)), 0, "size(diff(B, 2)) in test_diff_real_${k1}$ failed")
+        if (allocated(error)) return
+        call check(error, size(diff(B, 3)), 0, "size(diff(B, 3)) in test_diff_real_${k1}$ failed")
+        
     end subroutine test_diff_int_${k1}$
     #:endfor