Update src/stdlib_linalg_matrix_functions.fypp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: loiseaujc

src/stdlib_linalg_matrix_functions.fypp

@@ -43,10 +43,10 @@ contains
         lda = size(A, 1, kind=ilp) ; n = size(A, 2, kind=ilp)
         lde = size(E, 1, kind=ilp) ; ne = size(E, 2, kind=ilp)
 
-        if (lda<1 .or. n<1 .or. lda<n .or. lde<n .or. ne<n) then     
+        if (lda<1 .or. n<1 .or. lda/=n .or. lde/=n .or. ne/=n) then     
             err0 = linalg_state_type(this,LINALG_VALUE_ERROR, &
-                                     'invalid matrix sizes: A=',[lda,n], &
-                                                          ' E=',[lde,ne])
+                                     'invalid matrix sizes: A must be square (lda=', lda, ', n=', n, '), &
+                                     ' E must be square (lde=', lde, ', ne=', ne, ')')
         else
             E(:n, :n) = A(:n, :n) ; call stdlib_linalg_${ri}$_expm_inplace(E, order, err0)
         endif