DSIFA(3F)DSIFA(3F)NAMEDSIFA - 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 ,
follow DSIFA by DSISL. To compute DETERMINANT(A) , follow DSIFA by
DSIDI. To compute INERTIA(A) , follow DSIFA by DSIDI. To compute
INVERSE(A) , follow DSIFA by DSIDI.
SYNOPSYS
SUBROUTINE DSIFA(A,LDA,N,KPVT,INFO)
DESCRIPTION
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
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