I am trying to take in command line arguments with argv. I am using the command line argument to define a mesh size for a numerical integration program. Running the program looks like this

However, my program sets the mesh size to 0. I am sure I am screwing something up in the conversion of the string argv[1] to a double. Here is the relevant code:Code:mpiexec -n 4 ./ParallelSimpson .001

And here is the output:Code:/* * ParallelSimpson.c * Parallel Simpson's Rule * * Created by waterborne on 1/22/10. * Copyright 2010 __MyCompanyName__. All rights reserved. * */ #include "ParallelSimpson.h" int main(int argc, char* argv[]){ /* MPI constants */ int my_rank; // Rank of process int p; // Number of processes int source; // Rank of source int dest; // Rank of receiver int tag = 0; // Tag for messages float I_n; // Storage for integral value MPI_Status status; // Return status for receive /* Math constants */ float S_n = 0; // Partial sum for integral approximation float A, B; // Left and right endpoints respectively double h; // Mesh size float x1, x2, x3; // X values for each subinterval float sub_int_size; // (B - A) / p int n; // Iteration count int i; // Loop counter /* Start up MPI */ MPI_Init(&argc, &argv); /* Find out process rank */ MPI_Comm_rank(MPI_COMM_WORLD, &my_rank); /* Find out number of processes */ MPI_Comm_size(MPI_COMM_WORLD, &p); /* Set mesh size */ if (argv[1] == NULL) { h = .000001; // Set default mesh size } else { h = atof( &argv[1]); printf("argc: %d\n", argc); printf("Notice: mesh size set to %f\n", h); } /* Constant definitions */ A = -1.2; B = .7; if (A > B) { printf("Error: invalid interval\nQuitting..."); // Check interval return 1; } sub_int_size = (B - A) / p; n = (B - A) / (h * p); if (n % 2 == 0) { // Make sure n is odd n += 1; } /* Simpson's rule loop */ for (i = 0; i < n ; i += 2) { x1 = A + (sub_int_size * my_rank) + i * h; x2 = A + (sub_int_size * my_rank) + (i + 1) * h; x3 = A + (sub_int_size * my_rank) + (i + 2) * h; S_n += SimpEval(x1, x2, x3); } S_n *= h / 3.0; printf("Process %d calculated:: %f\n", my_rank, S_n); /* Sum results into I_n */ MPI_Reduce( &S_n, &I_n, 1, MPI_FLOAT, MPI_SUM, 0, MPI_COMM_WORLD); if (my_rank == 0) { printf("Approximation is: %f\n", I_n); } /* Shut down MPI */ MPI_Finalize(); return 0; } float SimpEval( float x1, float x2, float x3){ float y; // Returned value of Simpson rule over interval [x1,x3] y = f(x1) + 4 * f(x2) + f(x3); return y; } float f( float x){ float y; // Returned value of function y = pow(x, 3.0); // f(x) = x^3 return y; }

Where am I screwing up? ThanksCode:argc: 2 Notice: mesh size set to 0.000000 Process 0 calculated:: 0.000000 argc: 2 Notice: mesh size set to 0.000000 Process 1 calculated:: 0.000000 Approximation is: 0.000000 argc: 2 Notice: mesh size set to 0.000000 Process 2 calculated:: 0.000000 argc: 2 Notice: mesh size set to 0.000000 Process 3 calculated:: 0.000000