# 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
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

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