SSIDI(3F)SSIDI(3F)NAMESSIDI - SSIDI computes the determinant, inertia and inverse of a real
symmetric matrix using the factors from SSIFA.
SYNOPSYS
SUBROUTINE SSIDI(A,LDA,N,KPVT,DET,INERT,WORK,JOB)
DESCRIPTION
On Entry
A REAL(LDA,N)
the output from SSIFA.
LDA INTEGER
the leading dimension of the array A.
N INTEGER
the order of the matrix A.
KPVT INTEGER(N)
the pivot vector from SSIFA.
WORK REAL(N)
work vector. Contents destroyed.
JOB INTEGER
JOB has the decimal expansion ABC where
If C .NE. 0, the inverse is computed,
If B .NE. 0, the determinant is computed,
If A .NE. 0, the inertia is computed.
For example, JOB = 111 gives all three. On Return Variables not
requested by JOB are not used.
A contains the upper triangle of the inverse of
the original matrix. The strict lower triangle
is never referenced.
DET REAL(2)
determinant of original matrix.
Determinant = DET(1) * 10.0**DET(2)
with 1.0 .LE. ABS(DET(1)) .LT. 10.0
or DET(1) = 0.0.
INERT INTEGER(3)
the inertia of the original matrix.
INERT(1) = number of positive eigenvalues.
INERT(2) = number of negative eigenvalues.
INERT(3) = number of zero eigenvalues. Error Condition
A division by zero may occur if the inverse is requested and SSICO has
set RCOND .EQ. 0.0 or SSIFA has set INFO .NE. 0 . LINPACK. This
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SSIDI(3F)SSIDI(3F)
version dated 08/14/78 . James Bunch, Univ. Calif. San Diego, Argonne
Nat. Lab Subroutines and Functions BLAS SAXPY,SCOPY,SDOT,SSWAP Fortran
ABS,IABS,MOD
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