Question

#pragma omp parallel for要求循环变量是一个整数。那么如果循环变量不是整数，会发生什么呢？如本例所示？

    #include <stdio.h>
    #include <math.h>

    #define START (M_PI/2)
    #define END (M_PI*2)

    double f(double x)
    { return sin(x/2)+1;
    }

    int main(int argc, char *argv[])
    { double total = 0, x;
    int partitions;
    double slice;

    printf("How many partitions? "); fflush(stdout);
    scanf("%d", &partitions);
    slice = (END-START)/partitions;
    for (x = START + (slice/2); x < END; x = x + slice)
    total = total + f(x);
    total = total * slice;

    printf("The integration is %1.20f\n", total);
    }

如何将此程序转换为OpenMP？感谢

Answer 1

首先，您应该对代码的样式更加小心，尤其是缩进。代码如

for (x = START + (slice/2); x < END; x = x + slice)
total = total + f(x);
total = total * slice;

可能会产生误导，并且在将其写成

时会让您的生活更轻松

for (x = START + (slice/2); x < END; x = x + slice) {
  total = total + f(x);
}
total = total * slice;

代替。

关于你的问题，正如安德鲁所提到的，你可以通过用整数变量循环遍历分区来完全避免它，即

#pragma omp parallel for private(x) reduction(+:total)
for(int i = 0; i < partitions; i++) {
  x = START + slice/2 + i*slice;
  total = total + f(x);
}
total = total * slice;

OpenMP：如果循环变量不是整数，会发生什么情况，如本例所示？

1 个答案: