You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
109 lines
2.7 KiB
109 lines
2.7 KiB
/*
|
|
* =============================================================
|
|
* pagerank_gs_mult.c Compute the matrix vector multiplication
|
|
* for the gauss seidel iteration in an efficient manner
|
|
* (that is, by overwriting the vector x in place.)
|
|
*
|
|
* David Gleich
|
|
* Stanford University
|
|
* 28 January 2006
|
|
* =============================================================
|
|
*/
|
|
|
|
#include "mex.h"
|
|
|
|
/*
|
|
* The mex function just computes one matrix-vector product.
|
|
*/
|
|
void mexFunction(int nlhs, mxArray *plhs[],
|
|
int nrhs, const mxArray *prhs[])
|
|
{
|
|
int i, j, k;
|
|
int n, mrows, ncols;
|
|
|
|
/* sparse matrix */
|
|
int A_nz;
|
|
int *A_row, *A_col;
|
|
double *A_val;
|
|
|
|
double *x, *b;
|
|
double *xold;
|
|
|
|
if (nrhs != 3)
|
|
{
|
|
mexErrMsgTxt("Three inputs required.");
|
|
}
|
|
else if (nlhs > 1)
|
|
{
|
|
mexErrMsgTxt("Too many output arguments");
|
|
}
|
|
|
|
mrows = mxGetM(prhs[0]);
|
|
ncols = mxGetN(prhs[0]);
|
|
if (mrows != ncols ||
|
|
!mxIsSparse(prhs[0]) ||
|
|
!mxIsDouble(prhs[0]) ||
|
|
mxIsComplex(prhs[0]))
|
|
{
|
|
mexErrMsgTxt("Input must be a noncomplex square sparse matrix.");
|
|
}
|
|
|
|
/* okay, the first input passes */
|
|
n = mrows;
|
|
|
|
/* The second input must be a vector. */
|
|
if (mxGetM(prhs[1])*mxGetN(prhs[1]) != n ||
|
|
mxIsSparse(prhs[1]) || !mxIsDouble(prhs[1]))
|
|
{
|
|
mexErrMsgTxt("Invalid vector.");
|
|
}
|
|
|
|
/* The third input must be a vector. */
|
|
if (mxGetM(prhs[2])*mxGetN(prhs[2]) != n ||
|
|
mxIsSparse(prhs[2]) || !mxIsDouble(prhs[2]))
|
|
{
|
|
mexErrMsgTxt("Invalid vector.");
|
|
}
|
|
|
|
/* Get the sparse matrix */
|
|
A_nz = mxGetNzmax(prhs[0]);
|
|
A_val = mxGetPr(prhs[0]);
|
|
A_row = mxGetIr(prhs[0]);
|
|
A_col = mxGetJc(prhs[0]);
|
|
|
|
/* Get the vector x */
|
|
x = mxGetPr(prhs[1]);
|
|
|
|
/* Get the vector b */
|
|
b = mxGetPr(prhs[2]);
|
|
|
|
/* if they request x old, then we need to copy x to xold */
|
|
if (nlhs > 0)
|
|
{
|
|
plhs[0] = mxDuplicateArray(prhs[1]);
|
|
}
|
|
|
|
/* Update x in place, this means we have to iterate over columns
|
|
* of the matrix A. */
|
|
|
|
for (i = 0; i < n; i++)
|
|
{
|
|
/* we actually compute one iteration for the
|
|
* system (I+A')x = b */
|
|
double aself = 1.0;
|
|
double xnew = b[i];
|
|
|
|
|
|
for (j = A_col[i]; j < A_col[i+1]; ++j)
|
|
{
|
|
/* add to aself only if the row = i (the column) */
|
|
aself += A_val[j]*(A_row[j] == i);
|
|
|
|
/* add to xnew only if row != i */
|
|
xnew -= A_val[j]*x[A_row[j]]*(A_row[j] != i);
|
|
}
|
|
|
|
x[i] = xnew/aself;
|
|
}
|
|
}
|
|
|
|
|