#include "blaswrap.h" #include "f2c.h" /* Subroutine */ int dpptri_(char *uplo, integer *n, doublereal *ap, integer * info) { /* -- LAPACK routine (version 3.0) -- Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., Courant Institute, Argonne National Lab, and Rice University March 31, 1993 Purpose ======= DPPTRI 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 DPPTRF. Arguments ========= UPLO (input) CHARACTER*1 = 'U': Upper triangular factor is stored in AP; = 'L': Lower triangular factor is stored in AP. 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 triangular factor U or L from the Cholesky factorization A = U**T*U or A = L*L**T, packed columnwise as a linear array. The j-th column of U or L is stored in the array AP as follows: if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n. On exit, the upper or lower triangle of the (symmetric) inverse of A, overwriting the input factor U or L. 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. ===================================================================== Test the input parameters. Parameter adjustments */ /* Table of constant values */ static doublereal c_b8 = 1.; static integer c__1 = 1; /* System generated locals */ integer i__1, i__2; /* Local variables */ extern doublereal ddot_(integer *, doublereal *, integer *, doublereal *, integer *); extern /* Subroutine */ int dspr_(char *, integer *, doublereal *, doublereal *, integer *, doublereal *); static integer j; extern /* Subroutine */ int dscal_(integer *, doublereal *, doublereal *, integer *); extern logical lsame_(char *, char *); extern /* Subroutine */ int dtpmv_(char *, char *, char *, integer *, doublereal *, doublereal *, integer *); static logical upper; static integer jc, jj; extern /* Subroutine */ int xerbla_(char *, integer *), dtptri_( char *, char *, integer *, doublereal *, integer *); static doublereal ajj; static integer jjn; --ap; /* Function Body */ *info = 0; upper = lsame_(uplo, "U"); if (! upper && ! lsame_(uplo, "L")) { *info = -1; } else if (*n < 0) { *info = -2; } if (*info != 0) { i__1 = -(*info); xerbla_("DPPTRI", &i__1); return 0; } /* Quick return if possible */ if (*n == 0) { return 0; } /* Invert the triangular Cholesky factor U or L. */ dtptri_(uplo, "Non-unit", n, &ap[1], info); if (*info > 0) { return 0; } if (upper) { /* Compute the product inv(U) * inv(U)'. */ jj = 0; i__1 = *n; for (j = 1; j <= i__1; ++j) { jc = jj + 1; jj += j; if (j > 1) { i__2 = j - 1; dspr_("Upper", &i__2, &c_b8, &ap[jc], &c__1, &ap[1]); } ajj = ap[jj]; dscal_(&j, &ajj, &ap[jc], &c__1); /* L10: */ } } else { /* Compute the product inv(L)' * inv(L). */ jj = 1; i__1 = *n; for (j = 1; j <= i__1; ++j) { jjn = jj + *n - j + 1; i__2 = *n - j + 1; ap[jj] = ddot_(&i__2, &ap[jj], &c__1, &ap[jj], &c__1); if (j < *n) { i__2 = *n - j; dtpmv_("Lower", "Transpose", "Non-unit", &i__2, &ap[jjn], &ap[ jj + 1], &c__1); } jj = jjn; /* L20: */ } } return 0; /* End of DPPTRI */ } /* dpptri_ */