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LAPACKE_dgels Example Program in C for Row Major Data Layout
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/*
LAPACKE_dgels Example.
======================
Program computes the least squares solution to the overdetermined linear
system A*X = B with full rank matrix A using QR factorization,
where A is the coefficient matrix:
1.44 -7.84 -4.39 4.53
-9.96 -0.28 -3.24 3.83
-7.55 3.24 6.27 -6.64
8.34 8.09 5.28 2.06
7.08 2.52 0.74 -2.47
-5.45 -5.70 -1.19 4.70
and B is the right-hand side matrix:
8.58 9.35
8.26 -4.43
8.48 -0.70
-5.28 -0.26
5.72 -7.36
8.93 -2.52
Description.
============
The routine solves overdetermined or underdetermined real linear systems
involving an m-by-n matrix A, or its transpose, using a QR or LQ
factorization of A. It is assumed that A has full rank.
Several right hand side vectors b and solution vectors x can be handled
in a single call; they are stored as the columns of the m-by-nrhs right
hand side matrix B and the n-by-nrhs solution matrix X.
Example Program Results.
========================
LAPACKE_dgels (row-major, high-level) Example Program Results
Solution
-0.45 0.25
-0.85 -0.90
0.71 0.63
0.13 0.14
Residual sum of squares for the solution
195.36 107.06
Details of QR factorization
-17.54 -4.76 -1.96 0.42
-0.52 12.40 7.88 -5.84
-0.40 -0.14 -5.75 4.11
0.44 -0.66 -0.20 -7.78
0.37 -0.26 -0.17 -0.15
-0.29 0.46 0.41 0.24
*/
#include <stdlib.h>
#include <stdio.h>
#include "mkl_lapacke.h"
/* Auxiliary routines prototypes */
extern void print_matrix( char* desc, MKL_INT m, MKL_INT n, double* a, MKL_INT lda );
extern void print_vector_norm( char* desc, MKL_INT m, MKL_INT n, double* a, MKL_INT lda );
/* Parameters */
#define M 6
#define N 4
#define NRHS 2
#define LDA N
#define LDB NRHS
/* Main program */
int main() {
/* Locals */
MKL_INT m = M, n = N, nrhs = NRHS, lda = LDA, ldb = LDB, info;
/* Local arrays */
double a[LDA*M] = {
1.44, -7.84, -4.39, 4.53,
-9.96, -0.28, -3.24, 3.83,
-7.55, 3.24, 6.27, -6.64,
8.34, 8.09, 5.28, 2.06,
7.08, 2.52, 0.74, -2.47,
-5.45, -5.70, -1.19, 4.70
};
double b[LDB*M] = {
8.58, 9.35,
8.26, -4.43,
8.48, -0.70,
-5.28, -0.26,
5.72, -7.36,
8.93, -2.52
};
/* Executable statements */
printf( "LAPACKE_dgels (row-major, high-level) Example Program Results\n" );
/* Solve the equations A*X = B */
info = LAPACKE_dgels( LAPACK_ROW_MAJOR, 'N', m, n, nrhs, a, lda,
b, ldb );
/* Check for the full rank */
if( info > 0 ) {
printf( "The diagonal element %i of the triangular factor ", info );
printf( "of A is zero, so that A does not have full rank;\n" );
printf( "the least squares solution could not be computed.\n" );
exit( 1 );
}
/* Print least squares solution */
print_matrix( "Least squares solution", n, nrhs, b, ldb );
/* Print residual sum of squares for the solution */
print_vector_norm( "Residual sum of squares for the solution", m-n, nrhs,
&b[n*ldb], ldb );
/* Print details of QR factorization */
print_matrix( "Details of QR factorization", m, n, a, lda );
exit( 0 );
} /* End of LAPACKE_dgels Example */
/* Auxiliary routine: printing a matrix */
void print_matrix( char* desc, MKL_INT m, MKL_INT n, double* a, MKL_INT lda ) {
MKL_INT i, j;
printf( "\n %s\n", desc );
for( i = 0; i < m; i++ ) {
for( j = 0; j < n; j++ ) printf( " %6.2f", a[i*lda+j] );
printf( "\n" );
}
}
/* Auxiliary routine: printing norms of matrix columns */
void print_vector_norm( char* desc, MKL_INT m, MKL_INT n, double* a, MKL_INT lda ) {
MKL_INT i, j;
double norm;
printf( "\n %s\n", desc );
for( j = 0; j < n; j++ ) {
norm = 0.0;
for( i = 0; i < m; i++ ) norm += a[i*lda+j] * a[i*lda+j];
printf( " %6.2f", norm );
}
printf( "\n" );
}
Parent topic: DGELS Example