Convert symmetric matrix between packed and full storage?

Question

I\'m new to numerical linear algebra, and I have just started using LAPACK and BLAS.

Is there a routine that can copy/convert a symmetric matrix between packed and f

Answer 1

The obvious solution is to symmetrize the matrix by a "home-made/diy" code, the risk being to re-invent the wheel. It is pretty easy to write the for loops needed to symmetrize the matrix after dtpttr.

for(i=0;i

Is it efficient enough for your application ? On a 10000x10000 matrix, these for loops last 0.88s on my PC, while dtpttr lasts 0.24s.

Here is the test code. Compile it with gcc main.c -o main -llapack -lblas -lm :

#include 
#include 
#include 
#include 

void dtrttp_(char* UPLO,int* N,double* A,int* LDA,double* AP,int* INFO);
void dtpttr_(char* UPLO,int* N,double* AP,double* A,int* LDA,int* INFO);
void daxpy_(int* N,double* DA,double* DX,int* INCX,double* DY,int* INCY);

void dtpttf_(char* TRANSR,char* UPLO,int* N,double* AP,double* ARF,int* INFO);

int main(int argc, char **argv)
{

    int n=10;
    int info;

    double *a=malloc(n*n*sizeof(double));
    double *packed=malloc((n*(n+1))/2*sizeof(double));

    int i,j;
    for(i=0;i