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

```
DPOCO(3F)							     DPOCO(3F)

```

### NAME[Toc][Back]

```     DPOCO   - DPOCO factors a double precision	symmetric positive definite
matrix and	estimates the condition	of the matrix.

If	 RCOND	is not needed, DPOFA is	slightly faster.  To solve  A*X	= B ,
follow DPOCO by DPOSL.  To	compute	 INVERSE(A)*C ,	follow DPOCO by	DPOSL.
To	compute	 DETERMINANT(A)	, follow DPOCO by DPODI.  To compute
INVERSE(A)	, follow DPOCO by DPODI.

```

### SYNOPSYS[Toc][Back]

```      SUBROUTINE DPOCO(A,LDA,N,RCOND,Z,INFO)
```

### DESCRIPTION[Toc][Back]

```     On	Entry

A DOUBLE PRECISION(LDA, N)
the symmetric matrix to	be factored.  Only the
diagonal and upper triangle are	used.

LDA INTEGER
the leading dimension of the array  A .

N INTEGER
the order of the matrix	 A .  On Return

A an upper	triangular matrix  R  so that  A = TRANS(R)*R
where  TRANS(R)	 is the	transpose.
The strict lower triangle is unaltered.
If  INFO .NE. 0	, the factorization is not complete.

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.  If	INFO .NE. 0 , RCOND is unchanged.

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) .
If  INFO .NE. 0	, Z  is	unchanged.

INFO INTEGER
= 0  for normal	return.

Page 1

DPOCO(3F)							     DPOCO(3F)

= K  signals an	error condition.  The leading minor
of order  K  is	not positive definite.	LINPACK.  This version dated
08/14/78 .	 Cleve Moler, University of New	Mexico,	Argonne	National Lab.
Subroutines and Functions LINPACK DPOFA BLAS DAXPY,DDOT,DSCAL,DASUM
Fortran DABS,DMAX1,DREAL,DSIGN

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