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

```
DSIFA(3F)							     DSIFA(3F)

```

### NAME[Toc][Back]

```     DSIFA   - DSIFA factors a double precision	symmetric matrix by
elimination with symmetric	pivoting.

To	solve  A*X = B , follow	DSIFA by DSISL.	 To compute  INVERSE(A)*C ,
DSIDI.  To	compute	 INERTIA(A) , follow DSIFA by DSIDI.  To compute
INVERSE(A)	, follow DSIFA by DSIDI.

```

### SYNOPSYS[Toc][Back]

```      SUBROUTINE DSIFA(A,LDA,N,KPVT,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 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.

INFO INTEGER
= 0  normal value.
= K  if	the K-th pivot block is	singular.  This	is
not an error condition for this	subroutine,
but it does indicate that DSISL	or DSIDI may
divide by zero if called.  LINPACK.  This version dated	08/14/78 .
James Bunch, Univ.	Calif. San Diego, Argonne Nat. Lab.  Subroutines and
Functions BLAS DAXPY,DSWAP,IDAMAX Fortran DABS,DMAX1,DSQRT

PPPPaaaaggggeeee 1111```
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