no need for this ifdef, everything here is MPI anyway

src/elpa_generalized/cannon_back_template.c

@@ -418,7 +418,6 @@ void cannons_triang_rectangular_impl(math_type* U, math_type* B, int np_rows, in
 void cannons_triang_rectangular_c_impl(math_type* U, math_type* B, int local_rows, int local_cols,
                                     int* u_desc, int* b_desc, math_type *Res, int row_comm, int col_comm)
 {
-#ifdef WITH_MPI
   MPI_Comm c_row_comm = MPI_Comm_f2c(row_comm);
   MPI_Comm c_col_comm = MPI_Comm_f2c(col_comm);
 
@@ -435,9 +434,5 @@ void cannons_triang_rectangular_c_impl(math_type* U, math_type* B, int local_row
   // (order is swapped in the following call)
   // It is a bit unfortunate, maybe it should be changed in the Cannon algorithm to comply with ELPA standard notation?
   cannons_triang_rectangular_impl(U, B, np_rows, np_cols, my_prow, my_pcol, u_desc, b_desc, Res, c_col_comm, c_row_comm);
-#else
-  printf("Internal error: Cannons algorithm should not be called without MPI, stopping...\n");
-  exit(1);
-#endif
 }
 

src/elpa_generalized/cannon_forw_template.c

@@ -885,7 +885,6 @@ void cannons_reduction_impl(math_type* A, math_type* U, int np_rows, int np_cols
 void cannons_reduction_c_impl(math_type* A, math_type* U, int local_rows, int local_cols,
                          int* a_desc, math_type *Res, int ToStore, int row_comm, int col_comm)
 {
-#ifdef WITH_MPI
   MPI_Comm c_row_comm = MPI_Comm_f2c(row_comm);
   MPI_Comm c_col_comm = MPI_Comm_f2c(col_comm);
 
@@ -901,9 +900,5 @@ void cannons_reduction_c_impl(math_type* A, math_type* U, int local_rows, int lo
   // (order is swapped in the following call)
   // It is a bit unfortunate, maybe it should be changed in the Cannon algorithm to comply with ELPA standard notation?
   cannons_reduction_impl(A, U, np_rows, np_cols, my_prow, my_pcol, a_desc, Res, ToStore, c_col_comm, c_row_comm);
-#else
-  printf("Internal error: Cannons algorithm should not be called without MPI, stopping...\n");
-  exit(1);
-#endif
 }
 

src/elpa_impl_generalized_transform_template.F90

@@ -37,7 +37,7 @@
 
 #if !defined(WITH_MPI)
      if(my_p == 0) then
-       write(*,*) "Cannons algorithm can be used with MPI"
+       write(*,*) "Cannons algorithm can only be used with MPI"
        write(*,*) "Switching to elpa Hermitian and scalapack"
      end if
      use_cannon = 0