DSPTRI man page on IRIX

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DSPTRI(3F)							    DSPTRI(3F)

NAME
     DSPTRI - compute the inverse of a real symmetric indefinite matrix A in
     packed storage using the factorization A = U*D*U**T or A = L*D*L**T
     computed by DSPTRF

SYNOPSIS
     SUBROUTINE DSPTRI( UPLO, N, AP, IPIV, WORK, INFO )

	 CHARACTER	UPLO

	 INTEGER	INFO, N

	 INTEGER	IPIV( * )

	 DOUBLE		PRECISION AP( * ), WORK( * )

PURPOSE
     DSPTRI computes the inverse of a real symmetric indefinite matrix A in
     packed storage using the factorization A = U*D*U**T or A = L*D*L**T
     computed by DSPTRF.

ARGUMENTS
     UPLO    (input) CHARACTER*1
	     Specifies whether the details of the factorization are stored as
	     an upper or lower triangular matrix.  = 'U':  Upper triangular,
	     form is A = U*D*U**T;
	     = 'L':  Lower triangular, form is A = L*D*L**T.

     N	     (input) INTEGER
	     The order of the matrix A.	 N >= 0.

     AP	     (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2)
	     On entry, the block diagonal matrix D and the multipliers used to
	     obtain the factor U or L as computed by DSPTRF, stored as a
	     packed triangular matrix.

	     On exit, if INFO = 0, the (symmetric) inverse of the original
	     matrix, stored as a packed triangular matrix. The j-th column of
	     inv(A) is stored in the array AP as follows:  if UPLO = 'U', AP(i
	     + (j-1)*j/2) = inv(A)(i,j) for 1<=i<=j; if UPLO = 'L', AP(i +
	     (j-1)*(2n-j)/2) = inv(A)(i,j) for j<=i<=n.

     IPIV    (input) INTEGER array, dimension (N)
	     Details of the interchanges and the block structure of D as
	     determined by DSPTRF.

     WORK    (workspace) DOUBLE PRECISION array, dimension (N)

     INFO    (output) INTEGER
	     = 0: successful exit
	     < 0: if INFO = -i, the i-th argument had an illegal value

									Page 1

DSPTRI(3F)							    DSPTRI(3F)

	     > 0: if INFO = i, D(i,i) = 0; the matrix is singular and its
	     inverse could not be computed.

									Page 2

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