# ssvdch.f - Man Page

TESTING/EIG/ssvdch.f

## Synopsis

### Functions/Subroutines

subroutine **ssvdch** (n, s, e, svd, tol, info)**SSVDCH**

## Function/Subroutine Documentation

### subroutine ssvdch (integer n, real, dimension( * ) s, real, dimension( * ) e, real, dimension( * ) svd, real tol, integer info)

**SSVDCH**

**Purpose:**

SSVDCH checks to see if SVD(1) ,..., SVD(N) are accurate singular values of the bidiagonal matrix B with diagonal entries S(1) ,..., S(N) and superdiagonal entries E(1) ,..., E(N-1)). It does this by expanding each SVD(I) into an interval [SVD(I) * (1-EPS) , SVD(I) * (1+EPS)], merging overlapping intervals if any, and using Sturm sequences to count and verify whether each resulting interval has the correct number of singular values (using SSVDCT). Here EPS=TOL*MAX(N/10,1)*MACHEP, where MACHEP is the machine precision. The routine assumes the singular values are sorted with SVD(1) the largest and SVD(N) smallest. If each interval contains the correct number of singular values, INFO = 0 is returned, otherwise INFO is the index of the first singular value in the first bad interval.

**Parameters***N*N is INTEGER The dimension of the bidiagonal matrix B.

*S*S is REAL array, dimension (N) The diagonal entries of the bidiagonal matrix B.

*E*E is REAL array, dimension (N-1) The superdiagonal entries of the bidiagonal matrix B.

*SVD*SVD is REAL array, dimension (N) The computed singular values to be checked.

*TOL*TOL is REAL Error tolerance for checking, a multiplier of the machine precision.

*INFO*INFO is INTEGER =0 if the singular values are all correct (to within 1 +- TOL*MACHEPS) >0 if the interval containing the INFO-th singular value contains the incorrect number of singular values.

**Author**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **96** of file **ssvdch.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page ssvdch(3) is an alias of ssvdch.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK