# dlahilb.f - Man Page

TESTING/MATGEN/dlahilb.f

## Synopsis

### Functions/Subroutines

subroutine dlahilb (n, nrhs, a, lda, x, ldx, b, ldb, work, info)
DLAHILB

## Function/Subroutine Documentation

### subroutine dlahilb (integer n, integer nrhs, double precision, dimension(lda, n) a, integer lda, double precision, dimension(ldx, nrhs) x, integer ldx, double precision, dimension(ldb, nrhs) b, integer ldb, double precision, dimension(n) work, integer info)

DLAHILB

Purpose:

``` DLAHILB generates an N by N scaled Hilbert matrix in A along with
NRHS right-hand sides in B and solutions in X such that A*X=B.

The Hilbert matrix is scaled by M = LCM(1, 2, ..., 2*N-1) so that all
entries are integers.  The right-hand sides are the first NRHS
columns of M * the identity matrix, and the solutions are the
first NRHS columns of the inverse Hilbert matrix.

The condition number of the Hilbert matrix grows exponentially with
its size, roughly as O(e ** (3.5*N)).  Additionally, the inverse
Hilbert matrices beyond a relatively small dimension cannot be
generated exactly without extra precision.  Precision is exhausted
when the largest entry in the inverse Hilbert matrix is greater than
2 to the power of the number of bits in the fraction of the data type
used plus one, which is 24 for single precision.

In single, the generated solution is exact for N <= 6 and has
small componentwise error for 7 <= N <= 11.```
Parameters

N

```          N is INTEGER
The dimension of the matrix A.```

NRHS

```          NRHS is INTEGER
The requested number of right-hand sides.```

A

```          A is DOUBLE PRECISION array, dimension (LDA, N)
The generated scaled Hilbert matrix.```

LDA

```          LDA is INTEGER
The leading dimension of the array A.  LDA >= N.```

X

```          X is DOUBLE PRECISION array, dimension (LDX, NRHS)
The generated exact solutions.  Currently, the first NRHS
columns of the inverse Hilbert matrix.```

LDX

```          LDX is INTEGER
The leading dimension of the array X.  LDX >= N.```

B

```          B is DOUBLE PRECISION array, dimension (LDB, NRHS)
The generated right-hand sides.  Currently, the first NRHS
columns of LCM(1, 2, ..., 2*N-1) * the identity matrix.```

LDB

```          LDB is INTEGER
The leading dimension of the array B.  LDB >= N.```

WORK

`          WORK is DOUBLE PRECISION array, dimension (N)`

INFO

```          INFO is INTEGER
= 0: successful exit
= 1: N is too large; the data is still generated but may not
be not exact.
< 0: if INFO = -i, the i-th argument had an illegal value```
Author

Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Definition at line 123 of file dlahilb.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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

Tue Nov 28 2023 12:08:43 Version 3.12.0 LAPACK