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man pages->IRIX man pages -> complib/DGECO (3)
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### Contents

```
DGECO(3F)							     DGECO(3F)

```

### NAME[Toc][Back]

```     DGECO   - DGECO factors a double precision	matrix by Gaussian elimination
and estimates the condition of the	matrix.

If	 RCOND	is not needed, DGEFA is	slightly faster.  To solve  A*X	= B ,
follow DGECO by DGESL.  To	compute	 INVERSE(A)*C ,	follow DGECO by	DGESL.
To	compute	 DETERMINANT(A)	, follow DGECO by DGEDI.  To compute
INVERSE(A)	, follow DGECO by DGEDI.

```

### SYNOPSYS[Toc][Back]

```      SUBROUTINE DGECO(A,LDA,N,IPVT,RCOND,Z)
```

### DESCRIPTION[Toc][Back]

```     On	Entry

A DOUBLE PRECISION(LDA, N)
the matrix to be factored.

LDA INTEGER
the leading dimension of the array  A .

N INTEGER
the order of the matrix	 A .  On Return

A an upper	triangular matrix and the multipliers
which were used	to obtain it.
The factorization can be written  A = L*U  where
L  is a	product	of permutation and unit	lower
triangular matrices and	 U  is upper triangular.

IPVT INTEGER(N)
an INTEGER vector of pivot indices.

RCOND DOUBLE PRECISION
an estimate of the reciprocal condition	of  A .
For the	system	A*X = B	, relative perturbations
in  A  and  B  of size	EPSILON	 may cause
relative perturbations in  X  of size  EPSILON/RCOND .
If  RCOND  is so small that the	logical	expression
1.0 + RCOND .EQ. 1.0
is true, then  A  may be singular to working
precision.  In particular,  RCOND  is zero  if
exact singularity is detected or the estimate
underflows.

Z DOUBLE PRECISION(N)
a work vector whose contents are usually unimportant.
If  A  is close	to a singular matrix, then  Z  is
an approximate null vector in the sense	that
NORM(A*Z) = RCOND*NORM(A)*NORM(Z) .  LINPACK.  This version dated
08/14/78 .	 Cleve Moler, University of New	Mexico,	Argonne	National Lab.

Page 1

DGECO(3F)							     DGECO(3F)

Subroutines and Functions LINPACK DGEFA BLAS DAXPY,DDOT,DSCAL,DASUM
Fortran DABS,DMAX1,DSIGN

PPPPaaaaggggeeee 2222```
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