1 | // This is an alternative parallel version of quadrature_sequential.c |
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2 | // |
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3 | // It differs from quadratur_parallel.c by the way work is distributed. |
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4 | // This one uses a 'round robin' strategy. |
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5 | // |
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6 | // To compile: mpicc quadrature_parallel.c -lm |
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7 | // |
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8 | // This code also exhibits linear speedup. See listed output at the |
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9 | // bottom of this file. |
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10 | // |
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11 | // Ole Nielsen, SUT 2003 |
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12 | |
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13 | |
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14 | #include <math.h> |
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15 | #include <stdio.h> |
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16 | #include <time.h> |
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17 | #include <mpi.h> |
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18 | |
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19 | |
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20 | //Define the circle arc to be integrated. |
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21 | long double fct(long double x) { |
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22 | return sqrt(1.0-x*x); |
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23 | } |
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24 | |
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25 | |
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26 | int main(argc,argv) |
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27 | int argc; |
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28 | char *argv[]; |
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29 | { |
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30 | int N, i, lo, hi; |
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31 | long double result=0.0, my_result=0.0; |
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32 | long double reference = 3.1415926535897932; //Reference value, 17 digits |
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33 | |
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34 | |
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35 | double t0; |
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36 | int p; // Myid |
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37 | int P; // Number of processors |
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38 | |
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39 | int namelen, tag=0, j, k; |
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40 | char processor_name[MPI_MAX_PROCESSOR_NAME]; |
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41 | int *C; |
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42 | |
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43 | MPI_Status status; |
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44 | |
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45 | MPI_Init(&argc, &argv); |
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46 | MPI_Comm_rank(MPI_COMM_WORLD, &p); |
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47 | MPI_Comm_size(MPI_COMM_WORLD, &P); |
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48 | MPI_Get_processor_name(processor_name, &namelen); |
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49 | |
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50 | printf("This is process %d of %d running on %s\n", |
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51 | p, P, processor_name); |
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52 | |
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53 | N = 100000000; // Resolution |
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54 | //N = 29; // Resolution |
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55 | |
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56 | if (p == 0) { |
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57 | printf("Resolution = %d\n", N); |
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58 | } |
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59 | |
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60 | // Begin computation |
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61 | t0 = MPI_Wtime(); |
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62 | |
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63 | |
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64 | for (k=0; k<15; k++) { |
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65 | //Each process p handles own stride of points |
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66 | my_result = 0.0; |
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67 | for (i=p; i<N; i+=P) { |
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68 | my_result += fct( (i+0.5)/N ); |
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69 | } |
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70 | |
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71 | my_result = 4*my_result/N; |
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72 | } |
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73 | |
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74 | printf("P%d: Partial result = %.16Lf\n", p, my_result); |
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75 | |
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76 | |
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77 | // Communication phase |
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78 | if (p == 0) { |
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79 | |
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80 | //Receive results from others |
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81 | result = my_result; |
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82 | for (j=1; j<P; j++) { |
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83 | printf("P%d: receiving from P%d\n", p, j); |
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84 | MPI_Recv(&my_result, 1, MPI_LONG_DOUBLE, j, tag, |
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85 | MPI_COMM_WORLD, &status); |
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86 | result += my_result; |
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87 | } |
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88 | |
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89 | printf("Error = %.2e\n", fabs(result-reference)); |
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90 | printf("Time = %.2f sec\n", MPI_Wtime() - t0); |
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91 | |
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92 | } else { |
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93 | // send my_result to intended proc 0 |
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94 | MPI_Send(&my_result, 1, MPI_LONG_DOUBLE, 0, tag, |
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95 | MPI_COMM_WORLD); |
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96 | } |
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97 | |
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98 | MPI_Finalize(); |
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99 | return 0; |
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100 | } |
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101 | |
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102 | //Observed output, Resolution = 100000000 |
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103 | //P = 1 |
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104 | //Error = 3.44e-13 |
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105 | //Time = 13.52 sec |
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106 | // |
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107 | //P = 2 |
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108 | //Error = 3.44e-13 |
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109 | //Time = 6.76 sec |
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110 | // |
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111 | //P = 4 |
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112 | //Error = 3.44e-13 |
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113 | //Time = 3.39 sec |
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114 | // |
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115 | //P = 8 |
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116 | //Error = 3.44e-13 |
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117 | //Time = 1.69 sec |
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118 | // |
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119 | // |
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120 | //SPEEDUP & EFFICIENCY |
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121 | //t = array([13.52, 6.76, 3.39, 1.69]) |
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122 | // |
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123 | //t[0]/t |
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124 | // |
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125 | //array([ 1. , 2. , 3.98820059, 8. ]) |
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126 | // |
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127 | //p = [1, 2, 4, 8] |
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128 | // |
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129 | //t[0]/t/p |
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130 | //array([ 1. , 1. , 0.99705015, 1. ]) |
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131 | |
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132 | |
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133 | |
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134 | |
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