SUBROUTINE SPOTRI( UPLO, N, A, LDA, INFO ) * * -- LAPACK routine (version 3.1) -- * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. * November 2006 * * .. Scalar Arguments .. CHARACTER UPLO INTEGER INFO, LDA, N * .. * .. Array Arguments .. REAL A( LDA, * ) * .. * * Purpose * ======= * * SPOTRI computes the inverse of a real symmetric positive definite * matrix A using the Cholesky factorization A = U**T*U or A = L*L**T * computed by SPOTRF. * * Arguments * ========= * * UPLO (input) CHARACTER*1 * = 'U': Upper triangle of A is stored; * = 'L': Lower triangle of A is stored. * * N (input) INTEGER * The order of the matrix A. N >= 0. * * A (input/output) REAL array, dimension (LDA,N) * On entry, the triangular factor U or L from the Cholesky * factorization A = U**T*U or A = L*L**T, as computed by * SPOTRF. * On exit, the upper or lower triangle of the (symmetric) * inverse of A, overwriting the input factor U or L. * * LDA (input) INTEGER * The leading dimension of the array A. LDA >= max(1,N). * * INFO (output) INTEGER * = 0: successful exit * < 0: if INFO = -i, the i-th argument had an illegal value * > 0: if INFO = i, the (i,i) element of the factor U or L is * zero, and the inverse could not be computed. * * ===================================================================== * * .. External Functions .. LOGICAL LSAME EXTERNAL LSAME * .. * .. External Subroutines .. EXTERNAL SLAUUM, STRTRI, XERBLA * .. * .. Intrinsic Functions .. INTRINSIC MAX * .. * .. Executable Statements .. * * Test the input parameters. * INFO = 0 IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN INFO = -1 ELSE IF( N.LT.0 ) THEN INFO = -2 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN INFO = -4 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'SPOTRI', -INFO ) RETURN END IF * * Quick return if possible * IF( N.EQ.0 ) \$ RETURN * * Invert the triangular Cholesky factor U or L. * CALL STRTRI( UPLO, 'Non-unit', N, A, LDA, INFO ) IF( INFO.GT.0 ) \$ RETURN * * Form inv(U)*inv(U)' or inv(L)'*inv(L). * CALL SLAUUM( UPLO, N, A, LDA, INFO ) * RETURN * * End of SPOTRI * END