lin_svd_gen
Computes the SVD, A = USVT, of a real rectangular matrix A. An approximate generalized inverse and rank of A also can be computed.
Synopsis
#include <imsl.h>
float *imsl_f_lin_svd_gen (int m, int n, float a[], …, 0)
The type double procedure is imsl_d_lin_svd_gen.
Required Arguments
int m (Input)
Number of rows in the matrix.
int n (Input)
Number of columns in the matrix.
float a[] (Input)
Array of size m × n containing the matrix.
Return Value
If no optional arguments are used, imsl_f_lin_svd_gen returns a pointer to an array of size min (m, n) containing the ordered singular values of the matrix. To release this space, use imsl_free. If no value can be computed, then NULL is returned.
Synopsis with Optional Arguments
#include <imsl.h>
float *imsl_f_lin_svd_gen (int m, int n, float a[],
IMSL_A_COL_DIM, int a_col_dim,
IMSL_RETURN_USER, float s[],
IMSL_RANK, float tol, int *rank,
IMSL_U, float **p_u,
IMSL_U_USER, float u[],
IMSL_U_COL_DIM, int u_col_dim,
IMSL_V, float **p_v,
IMSL_V_USER, float v[],
IMSL_V_COL_DIM, int v_col_dim,
IMSL_INVERSE, float **p_gen_inva,
IMSL_INVERSE_USER, float gen_inva[],
IMSL_INV_COL_DIM, int gen_inva_col_dim,
0)
Optional Arguments
IMSL_A_COL_DIM, int a_col_dim (Input)
The column dimension of the array a.
Default: a_col_dim = n
IMSL_RETURN_USER, float s[] (Output)
A user-allocated array of size min (m+1, n) containing the singular values of A in its first min (m, n) positions in nonincreasing order. If IMSL_RETURN_USER is used, the return value of imsl_f_lin_svd_gen is s.
IMSL_RANK, float tol, int *rank (Input/Output)
float tol (Input)
Scalar containing the tolerance used to determine when a singular value is negligible and replaced by the value zero. If tol > 0, then a singular value si i is considered negligible if si.i ≤ tol. If tol < 0, then a singular value si.i is considered negligible if si.i ≤ ∣tol∣*∥A∥∞. In this case, ∣tol∣ should be an estimate of relative error or uncertainty in the data.
int *rank (Input/Output)
Integer containing an estimate of the rank of A.
IMSL_U, float **p_u (Output)
**p_u: The address of a pointer to an array of size m × min (m, n) containing the min (m, n) left-singular vectors of A. On return, the necessary space is allocated by imsl_f_lin_svd_gen. Typically, float *p_u is declared, and &p_u is used as an argument.
IMSL_U_USER, float u[] (Output)
u[]: The address of a pointer to an array of size m × min (m, n) containing the min (m, n) left-singular vectors of A. If m ≥ n, the left-singular vectors can be returned using the storage locations of the array a.
IMSL_U_COL_DIM, int u_col_dim (Input)
The column dimension of the array containing the left-singular vectors.
Default: u_col_dim = min (m, n)
IMSL_V, float **p_v (Output)
**p_v: The address of a pointer to an array of size n × n containing the right singular vectors of A. On return, the necessary space is allocated by imsl_f_lin_svd_gen. Typically, float *p_v is declared, and &p_v is used as an argument.
IMSL_V_USER, float v[] (Output)
v[]: The address of a pointer to an array of size n × n containing the right singular vectors of A. The right-singular vectors can be returned using the storage locations of the array a. Note that the return of the left- and right-singular vectors cannot use the storage locations of a simultaneously.
IMSL_V_COL_DIM, int v_col_dim (Input)
The column dimension of the array containing the right-singular vectors.
Default: v_col_dim = n
IMSL_INVERSE, float **p_gen_inva (Output)
The address of a pointer to an array of size n × m containing the generalized inverse of the matrix A. On return, the necessary space is allocated by imsl_f_lin_svd_gen. Typically, float *p_gen_inva is declared, and &p_gen_inva is used as an argument.
IMSL_INVERSE_USER, float gen_inva[] (Output)
A user-allocated array of size n × m containing the general inverse of the matrix A.
IMSL_INV_COL_DIM, int gen_inva_col_dim (Input)
The column dimension of the array containing the general inverse of the matrix A.
Default: gen_inva_col_dim = m
Description
The function imsl_f_lin_svd_gen computes the singular value decomposition of a real matrix A. It first reduces the matrix A to a bidiagonal matrix B by pre- and post-multiplying Householder transformations. Then, the singular value decomposition of B is computed using the implicit-shifted QR algorithm. An estimate of the rank of the matrix A is obtained by finding the smallest integer k such that sk,k ≤ tol or sk,k ≤ ∣tol∣*∥A∥∞. Since si+1,i+1 ≤ si,i, it follows that all the si,i satisfy the same inequality for i = k, …, min (m, n) − 1. The rank is set to the value k − 1. If A = USVT, its generalized inverse is A+ = VS+ UT. Here,
Only singular values that are not negligible are reciprocated. If IMSL_INVERSE or IMSL_INVERSE_USER is specified, the function first computes the singular value decomposition of the matrix A. The generalized inverse is then computed. The function imsl_f_lin_svd_gen fails if the QR algorithm does not converge after 30 iterations isolating an individual singular value.
Examples
Example 1
This example computes the singular values of a real 6 × 4 matrix.
#include <imsl.h>
float a[] = {1.0, 2.0, 1.0, 4.0,
3.0, 2.0, 1.0, 3.0,
4.0, 3.0, 1.0, 4.0,
2.0, 1.0, 3.0, 1.0,
1.0, 5.0, 2.0, 2.0,
1.0, 2.0, 2.0, 3.0};
int main()
{
int m = 6, n = 4;
float *s;
/* Compute singular values */
s = imsl_f_lin_svd_gen (m, n, a, 0);
/* Print singular values */
imsl_f_write_matrix ("Singular values", 1, n, s, 0);
}
Output
Singular values
1 2 3 4
11.49 3.27 2.65 2.09
Example 2
This example computes the singular value decomposition of the 6 × 4 real matrix A. The singular values are returned in the user-provided array. The matrices U and V are returned in the space provided by the function imsl_f_lin_svd_gen.
#include <imsl.h>
float a[] = {1.0, 2.0, 1.0, 4.0,
3.0, 2.0, 1.0, 3.0,
4.0, 3.0, 1.0, 4.0,
2.0, 1.0, 3.0, 1.0,
1.0, 5.0, 2.0, 2.0,
1.0, 2.0, 2.0, 3.0};
int main()
{
int m = 6, n = 4;
float s[4], *p_u, *p_v;
/* Compute SVD */
imsl_f_lin_svd_gen (m, n, a,
IMSL_RETURN_USER, s,
IMSL_U, &p_u,
IMSL_V, &p_v,
0);
/* Print decomposition*/
imsl_f_write_matrix ("Singular values, S", 1, n, s, 0);
imsl_f_write_matrix ("Left singular vectors, U", m, n, p_u, 0);
imsl_f_write_matrix ("Right singular vectors, V", n, n, p_v, 0);
}
Output
Singular values, S
1 2 3 4
11.49 3.27 2.65 2.09
Left singular vectors, U
1 2 3 4
1 -0.3805 0.1197 0.4391 -0.5654
2 -0.4038 0.3451 -0.0566 0.2148
3 -0.5451 0.4293 0.0514 0.4321
4 -0.2648 -0.0683 -0.8839 -0.2153
5 -0.4463 -0.8168 0.1419 0.3213
6 -0.3546 -0.1021 -0.0043 -0.5458
Right singular vectors, V
1 2 3 4
1 -0.4443 0.5555 -0.4354 0.5518
2 -0.5581 -0.6543 0.2775 0.4283
3 -0.3244 -0.3514 -0.7321 -0.4851
4 -0.6212 0.3739 0.4444 -0.5261
Example 3
This example computes the rank and generalized inverse of a 3 × 2 matrix A. The rank and the 2 × 3 generalized inverse matrix A+ are printed.
#include <imsl.h>
#include <stdio.h>
float a[] =
{1.0, 0.0,
1.0, 1.0,
100.0, -50.0};
int main()
{
int m = 3, n = 2;
float tol;
float gen_inva[6];
float *s;
int rank;
/* Compute generalized inverse */
tol = 1.e-4;
s = imsl_f_lin_svd_gen (m, n, a,
IMSL_RANK, tol, &rank,
IMSL_INVERSE_USER, gen_inva,
IMSL_INV_COL_DIM, m,
0);
/* Print rank, singular values and */
/* generalized inverse. */
printf ("Rank of matrix = %2d", rank);
imsl_f_write_matrix ("Singular values", 1, n, s, 0);
imsl_f_write_matrix ("Generalized inverse", n, m, gen_inva,
IMSL_A_COL_DIM, m,
0);
}
Output
Rank of matrix = 2
Singular values
1 2
111.8 1.4
Generalized inverse
1 2 3
1 0.100 0.300 0.006
2 0.200 0.600 -0.008
Warning Errors
IMSL_SLOWCONVERGENT_MATRIX | Convergence cannot be reached after 30 iterations. |
