DLAS2 (3) - Linux Man Pages

dlas2.f -

SYNOPSIS

Functions/Subroutines

subroutine dlas2 (F, G, H, SSMIN, SSMAX)
DLAS2 computes singular values of a 2-by-2 triangular matrix.

Function/Subroutine Documentation

subroutine dlas2 (double precisionF, double precisionG, double precisionH, double precisionSSMIN, double precisionSSMAX)

DLAS2 computes singular values of a 2-by-2 triangular matrix.

Purpose:

``` DLAS2  computes the singular values of the 2-by-2 matrix
[  F   G  ]
[  0   H  ].
On return, SSMIN is the smaller singular value and SSMAX is the
larger singular value.
```

Parameters:

F

```          F is DOUBLE PRECISION
The (1,1) element of the 2-by-2 matrix.
```

G

```          G is DOUBLE PRECISION
The (1,2) element of the 2-by-2 matrix.
```

H

```          H is DOUBLE PRECISION
The (2,2) element of the 2-by-2 matrix.
```

SSMIN

```          SSMIN is DOUBLE PRECISION
The smaller singular value.
```

SSMAX

```          SSMAX is DOUBLE PRECISION
The larger singular value.
```

Author:

Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Date:

September 2012

Further Details:

```  Barring over/underflow, all output quantities are correct to within
a few units in the last place (ulps), even in the absence of a guard

In IEEE arithmetic, the code works correctly if one matrix element is
infinite.

Overflow will not occur unless the largest singular value itself
overflows, or is within a few ulps of overflow. (On machines with
partial overflow, like the Cray, overflow may occur if the largest
singular value is within a factor of 2 of overflow.)

Underflow is harmless if underflow is gradual. Otherwise, results
may correspond to a matrix modified by perturbations of size near
the underflow threshold.
```

Definition at line 108 of file dlas2.f.

Author

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