First and foremost, there are ways to debug an MPI application, which should really be your top priority. A general approach for multi-process applications is to pause at the beginning of your application e.g. with a getchar()
then attach to each process with a debugger as described here:
- compile, link and start running your MPI program (you may wish to put a
read
statement early on to hold the program while you do the next steps) - attach to one of the currently running MPI processes: Debug – Attach to Process brings up a dialogue box which lists Available Processes. You should see
NUM
instances (whereN
is frommpiexec -n NUM
) of your executable. Select all of these and click on Attach. You can now debug by adding breakpoints etc. To move between MPI processes use the Process drop-down menu just above the code listing.
Having said that, at least one of the problems is with this part: int **array = new int*[(close - start)*cols];
(in the receive part of the application). You allocate the first dimension but not the second, so all pointers in the first dimension are uninitialized.
Change it to something like:
int *array = new int[(close - start) * cols]; MPI_Recv(array, (close - start) *cols, MPI_INT, 0, 3, MPI_COMM_WORLD, MPI_STATUSES_IGNORE); for (int i = start; i < close; i++) { for (int j = 0; j < cols; j++) { cout << array[(i - start) * cols]; res += array[(i - start) * cols] * v_array[i]; cout << res; } } delete[] array;
Or if you really want to use a 2D array, copy the initialization code from the sending part:
int rows = close - start; int **array = new int*[rows]; int size1 = rows * cols; array[0] = new int[size1]; for (int j = 1; j < rows; j++) { array[j] = &array[0][j*cols]; }
The second problem is that v_array
, being a global is not initialized in your receiver processes. Remember that in MPI each process is an independent program. So you should initialize v_array
always, i.e. regardless of pro_id
.
for (int i = 0; i < rows; i++) { v_array[i] = 1; }
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