Merge pull request #1134 from JAi-SATHVIK/fix/diff-shape-destruction

fix(math): preserve non-differenced dimension shape in diff for 2D array

Author: jvdp1

src/math/stdlib_math_diff.fypp

@@ -91,7 +91,14 @@ contains
         size_work = size_x + size_prepend + size_append
 
         if (size_work <= n_) then
-            allocate(y(0, 0))
+            select case (dim_)
+            case (1)
+                allocate(y(0, size(x, 2)))
+            case (2)
+                allocate(y(size(x, 1), 0))
+            case default
+                error stop "diff_2: internal error: invalid dimension (dim_ must be 1 or 2)"
+            end select
             return
         end if