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

```
DSICO(3F)							     DSICO(3F)

```

### NAME[Toc][Back]

```     DSICO   - DSICO factors a double precision	symmetric matrix by
elimination with symmetric	pivoting and estimates the condition of	the
matrix.

If	 RCOND	is not needed, DSIFA is	slightly faster.  To solve  A*X	= B ,
follow DSICO by DSISL.  To	compute	 INVERSE(A)*C ,	follow DSICO by	DSISL.
To	compute	 INVERSE(A) , follow DSICO by DSIDI.  To compute
DETERMINANT(A) , follow DSICO by DSIDI.  To compute  INERTIA(A), follow
DSICO by DSIDI.

```

### SYNOPSYS[Toc][Back]

```      SUBROUTINE DSICO(A,LDA,N,KPVT,RCOND,Z)
```

### 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 .  Output

A a block diagonal	matrix and the multipliers which
were used to obtain it.
The factorization can be written  A = U*D*TRANS(U)
where  U  is a product of permutation and unit
upper triangular matrices, TRANS(U) is the
transpose of  U	, and  D  is block diagonal
with 1 by 1 and	2 by 2 blocks.

KPVT 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)

Page 1

DSICO(3F)							     DSICO(3F)

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.
Subroutines and Functions LINPACK DSIFA BLAS DAXPY,DDOT,DSCAL,DASUM
Fortran DABS,DMAX1,IABS,DSIGN

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