#include "blaswrap.h" #include "f2c.h" /* Subroutine */ int spptri_(char *uplo, integer *n, real *ap, integer *info) { /* -- LAPACK routine (version 3.1) -- Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. November 2006 Purpose ======= SPPTRI 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 SPPTRF. 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) REAL 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 real c_b8 = 1.f; static integer c__1 = 1; /* System generated locals */ integer i__1, i__2; /* Local variables */ static integer j, jc, jj; static real ajj; static integer jjn; extern doublereal sdot_(integer *, real *, integer *, real *, integer *); extern /* Subroutine */ int sspr_(char *, integer *, real *, real *, integer *, real *); extern logical lsame_(char *, char *); extern /* Subroutine */ int sscal_(integer *, real *, real *, integer *); static logical upper; extern /* Subroutine */ int stpmv_(char *, char *, char *, integer *, real *, real *, integer *), xerbla_(char * , integer *), stptri_(char *, char *, integer *, real *, integer *); --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_("SPPTRI", &i__1); return 0; } /* Quick return if possible */ if (*n == 0) { return 0; } /* Invert the triangular Cholesky factor U or L. */ stptri_(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; sspr_("Upper", &i__2, &c_b8, &ap[jc], &c__1, &ap[1]); } ajj = ap[jj]; sscal_(&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] = sdot_(&i__2, &ap[jj], &c__1, &ap[jj], &c__1); if (j < *n) { i__2 = *n - j; stpmv_("Lower", "Transpose", "Non-unit", &i__2, &ap[jjn], &ap[ jj + 1], &c__1); } jj = jjn; /* L20: */ } } return 0; /* End of SPPTRI */ } /* spptri_ */