package edu.emory.mathcs.csparsej.tdouble;
import edu.emory.mathcs.csparsej.tdouble.Dcs_common.Dcs;
/**
* Transpose a sparse matrix.
*
* @author Piotr Wendykier (piotr.wendykier@gmail.com)
*
*/
public class Dcs_transpose {
/**
* Computes the transpose of a sparse matrix, C =A';
*
* @param A
* column-compressed matrix
* @param values
* pattern only if false, both pattern and values otherwise
* @return C=A', null on error
*/
public static Dcs cs_transpose(Dcs A, boolean values) {
int p, q, j, Cp[], Ci[], n, m, Ap[], Ai[], w[];
double Cx[], Ax[];
Dcs C;
if (!Dcs_util.CS_CSC(A))
return (null); /* check inputs */
m = A.m;
n = A.n;
Ap = A.p;
Ai = A.i;
Ax = A.x;
C = Dcs_util.cs_spalloc(n, m, Ap[n], values && (Ax != null), false); /* allocate result */
w = new int[m]; /* get workspace */
Cp = C.p;
Ci = C.i;
Cx = C.x;
for (p = 0; p < Ap[n]; p++)
w[Ai[p]]++; /* row counts */
Dcs_cumsum.cs_cumsum(Cp, w, m); /* row pointers */
for (j = 0; j < n; j++) {
for (p = Ap[j]; p < Ap[j + 1]; p++) {
Ci[q = w[Ai[p]]++] = j; /* place A(i,j) as entry C(j,i) */
if (Cx != null)
Cx[q] = Ax[p];
}
}
return C;
}
}