updated 3

Author: srinjoy933

src/math/stdlib_math_diff.fypp

@@ -75,28 +75,22 @@ contains
 
         size_prepend = 0
         size_append = 0
+        
+        dim_ = 1
         if (present(dim)) then
-            if (dim == 1 .or. dim == 2) then
-                dim_ = dim
-            else
-                dim_ = 1
-            end if
-        else
-            dim_ = 1
+            if (dim == 1 .or. dim == 2) dim_ = dim
         end if
-        
+
         if (present(prepend)) then
             if (size(prepend, 3 - dim_) /= size(x, 3 - dim_)) then
-                allocate(y(0, 0))
-                return
+                error stop "stdlib_math_diff: non-differencing dimension of 'prepend' must match 'x'"
             end if
             size_prepend = size(prepend, dim_)
         end if
 
         if (present(append)) then
             if (size(append, 3 - dim_) /= size(x, 3 - dim_)) then
-                allocate(y(0, 0))
-                return
+                error stop "stdlib_math_diff: non-differencing dimension of 'append' must match 'x'"
             end if
             size_append = size(append, dim_)
         end if
@@ -110,8 +104,6 @@ contains
                 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