openmp

问题 I have the following code: const W = (f.IsUnit() ? U : modq.Multiply(m_pre_2_3q, U)); const Integer t = modp.Multiply(modp.Exponentiate(V, 3), eh); const X = (f.IsUnit() ? t : modp.Multiply(m_pre_2_9p, t)); When converted to OpenMP, the const-ness is lost: Integer W, X; #pragma omp parallel sections { #pragma omp section { W = (f.IsUnit() ? U : modq.Multiply(m_pre_2_3q, U)); } #pragma omp section { const Integer t = modp.Multiply(modp.Exponentiate(V, 3), eh); X = (f.IsUnit() ? t : modp

问题 System Specification: Intel Xeon E7-v3 Processor(4 sockets, 16 cores/sockets, 2 threads/core) Use of Eigen family and C++ Following is serial implementation of code snippet: Eigen::VectorXd get_Row(const int j, const int nColStart, const int nCols) { Eigen::VectorXd row(nCols); for (int k=0; k<nCols; ++k) { row(k) = get_Matrix_Entry(j,k+nColStart); } } double get_Matrix_Entry(int x , int y){ return exp(-(x-y)*(x-y)); } I need to parallelise the get_Row part as nCols can be as large as 10^6,

问题 At the first,I used the default gcc on my mac.but it does't support openmp. using " gcc -v ",I get gcc 4.2.1 So, I used brew to install gcc. When it is done, using the " gcc -v ",it has no changes. the brew give tips to me "openmp may not be supported,using " brew reinstall gcc --without-muli "?? I don't remember the "muli???" accurately.I try that,but It doesn't help. So, this is my question: What can I do to make my gcc to support openmp in my macbook? 回答1: Brew will install gcc under a

问题 I'm beginning in openMP and I want parallelize this portion of code : for (i=0 ;i<n ;i++) for (j=1 ;j<n ;j++) A[i][j]+=A[i][j-1]; and I find this answer: #pragma omp parallel for private(i, j) shared(A, n) for (i = 0; i < n; ++i) for (j = 1; j < n; ++j) A[i][j] += A[i][j-1]; I have some questions: why does i private and not shared? about this answer if i have 4 threads so each thread executes the same code, I don't understand how can I obtain a same result as sequential code ? How do threads

问题 I know that OpenMP is included in NDK (usage example here: http://recursify.com/blog/2013/08/09/openmp-on-android ). I've done what it says on that page but when I use: #pragma omp for on a simple for loop that scans a vector, the app crashes with the famous "fatal signal 11". What am I missing here? Btw I use a modified example from the Android samples, it's Tutorial 2 Mixed Processing. All I want is to parallelize (multithread) some of the for loops and nested for loops that I have in the

问题 I use Intel Xeon x2 (24 kernels) and Windows Server 2008. Trying to parallelize my c++ program. Template code here: vector< string > files; vector< vector< float > > data; ... data.resize( files.size() ); #pragma omp parallel for for (int i=0; i<files.size(); i++) { // Files count is about 3000 FILE *f = fopen(files[i].c_str(), "rb"); // every file is about 40 mb data[i].resize(someSize); fread(&data[i][0], sizeof(float), someSize, f); fclose(f); ... performCalculations(); } CPU Usage is only

问题 i have the following code : #pragma omp parallel sections num_threads(2) { #pragma omp section Function_1; #pragma omp section Function_2; } but within the Function_1 and Function_2, i have a parallel for but just one thread run it. So, how run the Function_1 and Function_2 in parallel and run several threads within these functions? thx! 回答1: Having one parallel region inside another is called nesting. By default nested regions are inactive, which means that they execute serially. In order to

问题 I am trying to add OpenMP parallelization to a working code (just to a single for loop), however I cannot get rid of a segmentation fault. The problem arises from this line: pos += sprintf(com + pos, "%d ", i); com is a character array, and I tried defining it as char com[255] or char *com = malloc(255*sizeof(char)) , both inside and before the for loop. I added private(com) to #pragma omp parallel for directive when I defined com before the loop. I also tried initializing it and using

问题 I am newbie in openmp. The following is the environment. OS : Mac OSX Mavericks Compiler : gcc (MacPorts gcc48 4.8.2_0) 4.8.2 IDE : Eclipse Kepler CDT plugin I wrote the following openmp program #include < stdio.h> #include < omp.h> int main() { #pragma omp parallel { int i=omp_get_thread_num(); printf("hello (%d)",i); printf("world (%d)",i); } } I compiled the above program and got the error that omp.h is not found and lgomp not found. Hence I added in the project properties an include path

问题 I would like to "nest" parallel for using OpenMP. Here is a toy code: #include <iostream> #include <cmath> void subproblem(int m) { #pragma omp parallel for for (int j{0}; j < m; ++j) { double sum{0.0}; for (int k{0}; k < 10000000; ++k) { sum += std::cos(static_cast<double>(k)); } #pragma omp critical { std::cout << "Sum: " << sum << std::endl; } } } int main(int argc, const char *argv[]) { int n{2}; int m{8}; #pragma omp parallel for for (int i{0}; i < n; ++i) { subproblem(m); } return 0; }