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322 ira 1 
#include <stdio.h>
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#include <limits.h>
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#include <mpi.h>
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const int ROOT_NODE = 0;
325 ira 6 
int numprocs;
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int myid;
322 ira 8 
 
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/**
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 * NOTE: Accessing "matrices" in this program is a little strange.
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 * I decided to implement matrices using an array. To get to a[row][col],
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 * you would use a[row*a_size+col]. Pretty simple actually.
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 */
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int* allocate (int rows, int cols)
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{
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    int *temp = NULL;
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    if ((temp = (int*) malloc (rows * cols * sizeof(int))) == NULL)
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        printf ("Could not allocate memory for array of size: %d x %d\n", rows, cols);
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    return temp;
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}
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325 ira 25 
void print_matrix (int *b, int n, const char *s)
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{
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    int i,j;
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    if (n<=10) // n<=10
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    {
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        printf ("%s\n", s);
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        for (i=0; i<n; i++)
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        {
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            for (j=0; j<n; j++)
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                printf ("%d\t", b[i*n+j]);
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            printf ("\n");
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        }
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        printf ("\n");
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    }
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    else if (n<=100) // 10<n<=100
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    {
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        printf ("%s\n", s);
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        // First 2 rows
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        for (i=0; i<2; i++)
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        {
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            for (j=0; j<n; j++)
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                printf ("%d\t", b[i*n+j]);
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            printf ("\n");
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        }
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        printf ("\n");
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        // First 2 cols
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        for (i=0; i<n; i++)
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        {
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            for (j=0; j<2; j++)
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                printf ("%d\t", b[i*n+j]);
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            printf ("\n");
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        }
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    }
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}
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void matrix_mult (int *b, int *c, int n)
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{
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    int i,j,k,ii,temp;
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    /* Multiply our slice of the matrix, store it in c */
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    for (ii=0; ii<n/numprocs; ii++)
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    {
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        i = ii + myid * n/numprocs; // i is the offset into b
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        for (j=0; j<n; j++)
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        {
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            // MATRIX_MULT
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            // c[i*n+j]=0;
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            // SHORTEST PATH
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            c[ii*n+j] = INT_MAX;
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            for (k=0; k<n; k++)
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            {
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                // MATRIX MULT
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                // c[i*n+j] += a[i*n+k] * b[k*n+j];
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                // SHORTEST PATH
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                if (b[i*n+k] == INT_MAX || b[k*n+j] == INT_MAX)
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                    temp = INT_MAX;
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                else
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                    temp = b[i*n+k] + b[k*n+j];
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                if (temp < c[ii*n+j])
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                    c[ii*n+j] = temp;
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            }
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        }
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    }
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}
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322 ira 102 
int main (int argc, char *argv[])
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{
324 ira 104 
    const int n = 4;
325 ira 105 
    int *b, *c;
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    int i, j, k, temp, t;
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    MPI_Status status;
322 ira 108 
 
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    /* Get all of the necessary info for each process */
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    MPI_Init (&argc, &argv);
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    MPI_Comm_rank (MPI_COMM_WORLD, &myid);
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    MPI_Comm_size (MPI_COMM_WORLD, &numprocs);
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    /* Allocate all of b for each process, since we'll need it */
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    b = allocate (n, n);
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117 
    if (myid == ROOT_NODE)
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    {
325 ira 119 
        /* Allocate the full c, since we need to initialize it */
322 ira 120 
        c = allocate (n, n);
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        /* Initialize values */
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        for (i=0; i<n; i++)
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            for (j=0; j<n; j++)
324 ira 125 
                b[i*n+j] = INT_MAX;
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323 ira 127 
        b[0] = 0;
324 ira 128 
        b[1] = 2;
323 ira 129 
        b[2] = INT_MAX;
324 ira 130 
        b[3] = 10;
323 ira 131 
 
324 ira 132 
        b[4] = 2;
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        b[5] = 0;
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        b[6] = 2;
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        b[7] = INT_MAX;
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137 
        b[8]  = INT_MAX;
138 
        b[9]  = 2;
139 
        b[10] = 0;
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        b[11] = 3;
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142 
        b[12] = 10;
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        b[13] = INT_MAX;
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        b[14] = 3;
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        b[15] = 0;
146 
 
325 ira 147 
        if (n<=100)
148 
            print_matrix (b, n, "Input Matrix:");
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        else
150 
        {
151 
            printf ("Beginning calculation for all shortest paths\n");
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            printf ("for a graph with %d nodes\n", n);
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        }
154 
 
322 ira 155 
    }
156 
    else
157 
    {
325 ira 158 
        /* Allocate our slice of c, since that's all we need */
322 ira 159 
        c = allocate (n/numprocs, n);
160 
    }
161 
 
325 ira 162 
    /* Send all of b to each process, since they need all of it */
322 ira 163 
    MPI_Bcast (b, n*n, MPI_INT, ROOT_NODE, MPI_COMM_WORLD);
164 
 
325 ira 165 
    /* Run our piece of the calculation.
166 
     * Synchronize data with all other processes at the end of each step. */
167 
    for (t=0; t<ceil(log(n-1)); t++)
322 ira 168 
    {
325 ira 169 
        matrix_mult (b, c, n);
170 
        MPI_Allgather (c, n*n/numprocs, MPI_INT, b, n*n/numprocs, MPI_INT, MPI_COMM_WORLD);
322 ira 171 
    }
172 
 
325 ira 173 
    /* Print out the result matrix. */
322 ira 174 
    if (myid == ROOT_NODE)
175 
    {
325 ira 176 
        if (n<=100)
177 
            print_matrix (b, n, "Result Matrix:");
178 
        else
323 ira 179 
        {
325 ira 180 
            printf ("Finished calculation for all shortest paths\n");
181 
            printf ("for a graph with %d nodes\n", n);
323 ira 182 
        }
322 ira 183 
    }
184 
 
185 
    /* Free all of the memory we allocated earlier */
186 
    free (b);
187 
    free (c);
188 
 
189 
    MPI_Finalize ();
190 
    return 0;
191 
}
192