BlaEigen.c

Go to the documentation of this file.

 
#include <math.h>
 
#include "fasp.h"
#include "fasp_functs.h"
 
/*---------------------------------*/
/*--      Public Functions       --*/
/*---------------------------------*/
 
REAL fasp_dcsr_maxeig (const dCSRmat  *A,
                       const REAL      tol,
                       const INT       maxit)
{
    REAL eigenvalue = 0.0, temp = 1.0, L2_norm_y;
    dvector x, y;
    int i;
 
    fasp_dvec_alloc(A->row, &x);
    fasp_dvec_rand(A->row,&x);
    fasp_blas_darray_ax(A->row, 1.0/fasp_blas_dvec_norm2(&x), x.val);
    
    fasp_dvec_alloc(A->row, &y);
    
    for ( i = maxit; i--; ) {
        // y = Ax;
        fasp_blas_dcsr_mxv(A, x.val, y.val);
        
        // y/||y||
        L2_norm_y = fasp_blas_dvec_norm2(&y);
        fasp_blas_darray_ax(A->row, 1.0/L2_norm_y, y.val);
        
        // eigenvalue = y'Ay;
        eigenvalue = fasp_blas_dcsr_vmv(A, y.val, y.val);
        
        // convergence test
        if ( (ABS(eigenvalue - temp)/ABS(temp)) < tol ) break;
        
        fasp_dvec_cp(&y, &x);
        temp = eigenvalue;
    }
    
    // clean up memory
    fasp_dvec_free(&x);
    fasp_dvec_free(&y);
    
    return eigenvalue;
}
 
/*---------------------------------*/
/*--        End of File          --*/
/*---------------------------------*/