openmp

问题 I am trying to compile a Fortran code including OpenMP. I am replicating the use of OpenMP from a different code. It built successfully once yesterday and then the next time I built it I get the following error: ../MAXBRG3D.f90:3:4: USE OMP_LIB ! USED WITH OMP FUNCTIONS 1 Fatal Error: Can't open module file 'omp_lib.mod' for reading at (1): No such file or directory compilation terminated. subdir.mk:329: recipe for target 'MAXBRG3D.o' failed make: *** [MAXBRG3D.o] Error 1 The only changes I

问题 How does OpenMP uses atomic instructions inside reduction constructor? Doesn't it rely on atomic instructions at all? For instance, is the variable sum in the code below accumulated with atomic '+' operator? #include <omp.h> #include <vector> using namespace std; int main() { int m = 1000000; vector<int> v(m); for (int i = 0; i < m; i++) v[i] = i; int sum = 0; #pragma omp parallel for reduction(+:sum) for (int i = 0; i < m; i++) sum += v[i]; } 回答1: How does OpenMP uses atomic instruction

问题 How does OpenMP uses atomic instructions inside reduction constructor? Doesn't it rely on atomic instructions at all? For instance, is the variable sum in the code below accumulated with atomic '+' operator? #include <omp.h> #include <vector> using namespace std; int main() { int m = 1000000; vector<int> v(m); for (int i = 0; i < m; i++) v[i] = i; int sum = 0; #pragma omp parallel for reduction(+:sum) for (int i = 0; i < m; i++) sum += v[i]; } 回答1: How does OpenMP uses atomic instruction

问题 Assume we want to count something in an OpenMP loop. Compare the reduction int counter = 0; #pragma omp for reduction( + : counter ) for (...) { ... counter++; } with the atomic increment int counter = 0; #pragma omp for for (...) { ... #pragma omp atomic counter++ } The atomic access provides the result immediately, while a reduction only assumes its correct value at the end of the loop. For instance, reductions do not allow this: int t = counter; if (t % 1000 == 0) { printf ("%dk iterations

问题 I have a series of calls to few independent functions. func1(arg); func2(arg); func3(arg); Instead of executing them serially, I want to execute them in parallel. I am currently using #pragma omp parallel { func1(arg); func2(arg); func3(arg) } Other ways I'm trying is using a switch case and then executing this in parallel to split the task to different threads like function(arg, value) { switch(value) { case 1: // code of func1 case 2: // code of func2 case 3 :// code of func3 } } #pragma

问题 I have a series of calls to few independent functions. func1(arg); func2(arg); func3(arg); Instead of executing them serially, I want to execute them in parallel. I am currently using #pragma omp parallel { func1(arg); func2(arg); func3(arg) } Other ways I'm trying is using a switch case and then executing this in parallel to split the task to different threads like function(arg, value) { switch(value) { case 1: // code of func1 case 2: // code of func2 case 3 :// code of func3 } } #pragma

问题 I have a nested loop, with few outer, and many inner iterations. In the inner loop, I need to calculate a sum, so I want to use an OpenMP reduction. The outer loop is on a container, so the reduction is supposed to happen on an element of that container. Here's a minimal contrived example: #include <omp.h> #include <vector> #include <iostream> int main(){ constexpr int n { 128 }; std::vector<int> vec (4, 0); for (unsigned int i {0}; i<vec.size(); ++i){ /* this does not work */ //#pragma omp

问题 when I use openmp like this: #pragma omp parallel for reduction(max: dumax) the IDE will raise an error "max" in Openmp "reduction" is invalid #pragma omp parallel for reduction(max: dumax) for (int i = 1; i < n + 1; i++) { for (int j = 1; j < n + 1; j++) { u[i][j] = 0.25 * u[i - 1][j] + 0.25 * u[i][j - 1] + 0.25 * u[i + 1][j] + 0.25 * u[i][j + 1] + h * h * f[i][j]; dumax = max(dumax, abs(u[i][j] - uold[i][j])); } } 回答1: MSVC compiler is stuck with OpenMP version 2.0, and unfortunately for

问题 I'm new to the concept of concurrent and parallel programing in general. I'm trying to calculate Pi using Monte Carlo method in C. Here is my source code: #include <stdio.h> #include <stdlib.h> #include <math.h> #include <time.h> int main(void) { long points; long m = 0; double coordinates[2]; double distance; printf("Enter the number of points: "); scanf("%ld", &points); srand((unsigned long) time(NULL)); for(long i = 0; i < points; i++) { coordinates[0] = ((double) rand() / (RAND_MAX));

问题 This question already has answers here : OpenMP Several “shared”-directives? (2 answers) Closed last month . I have a line of a Fortran code, e.g., !$omp do private(aa, bb, cc) schedule(dynamic) reduction(+:alpha, beta, gamma) Suppose this line contains several arguments and the length exceeds 132 characters, gfortran will lead to error message. I tried to use & to break the line. But I am not sure how to start the next line. As other case, directly start the next line without ! leads to