Add macro to report the MPI error

error.h

@@ -19,3 +19,15 @@ extern int myrank;
     printf("[%04i] %s %s: " s "\n", myrank, clocks_get_timesincestart(), \
            __FUNCTION__, ##__VA_ARGS__);                                 \
   })
+
+/* Print MPI error as a string. */
+#define mpi_error_string(res, s, ...)                                      \
+  ({                                                                       \
+    fprintf(stdout, "[%03i] %s %s:%s():%i: " s "\n", myrank,               \
+            clocks_get_timesincestart(), __FILE__, __FUNCTION__, __LINE__, \
+            ##__VA_ARGS__);                                                \
+    int len = 1024;                                                        \
+    char buf[len];                                                         \
+    MPI_Error_string(res, buf, &len);                                      \
+    fprintf(stdout, "%s\n\n", buf);                                        \
+  })