# ?gehss

Solves a system of interval linear equations by interval Householder method.

## Syntax

call sigehss(trans, n, nrhs, a, lda, b, ldb, info)

call digehss(trans, n, nrhs, a, lda, b, ldb, info)

## Description

The routine ?gehss uses the interval Householder method to compute an enclosure of the solution set to the following interval linear system of equations:

`A*X = B`, if `trans = 'N'`,

`AT*X = B`, if `trans = 'T'` or 'C'.

## Input Parameters

trans

  CHARACTER(1). Must be one of 'N', 'T', 'C', 'n', 't', or 'c'.

  Indicates the form of the equations system:

  If `trans = 'N'` or 'n', then `A*X = B` is solved for X.

  If `trans = 'T'` or 'C' or 't'or 'c', then `AT*X = B` is solved for X.

n

  INTEGER. The order of A, the number of rows in B (n ≥ 0).

nrhs

  INTEGER. The number of right-hand sides (nrhs ≥ 0).

a, b

  REAL for sigehss.

  DOUBLE PRECISION for digehss.

  Arrays: `a (lda,*)`, `b (ldb,*)`.

  The array a contains the matrix A.

  The array b contains the matrix B, whose columns are the right-hand sides for the systems of equations.

  The second dimension of a must be at least `max(1,n)` and the second dimension of b must be at least `max(1,nrhs)`.

lda

  INTEGER. The first dimension of a, `lda ≥ max(1, n)`.

ldb

  INTEGER. The first dimension of b, `ldb ≥ max(1, n)`.

## Output Parameters

b

  Overwritten by an enclosure of the solution matrix X.

info

  INTEGER.

  If `info = 0`, the execution is successful.

  If `info ≥ 0`, the execution is not successful.

  If `info = -i`, the i-th parameter has an illegal value.

Parent topic: Routines for Fast Solution of Interval Systems