Dtbcon Dtbtrs Dtpcon Dtptri Dtptrs Dtrcon Dtrtri Dtrtrs

Dtptri() Sub Dtptri ( Uplo As  String, Diag As  String, N As  Long, Ap() As  Double, Info As  Long  ) Inverse of a triangular matrix in packed form Purpose This routine computes the inverse of a real upper or lower triangular matrix A stored in packed form. Parameters [in] Uplo = "U": A is upper triangular. = "L": A is lower triangular. [in] Diag = "N": A is non-unit triangular. = "U": A is unit triangular. (Diagonal elements of Ap() are not referenced and are assumed to be 1) [in] N Order of the matrix A. (N >= 0) (If N = 0, returns without computation) [in] Ap() Array Ap(LAp - 1) (LAp >= N(N + 1)/2) [in] N x N triangular matrix A in packed symmetric matrix form. Upper or lower part is to be stored in accordance with Uplo. [out] The (triangular) inverse of the original matrix, in the same packed form. [out] Info = 0: Successful exit. = -1: The argument Uplo had an illegal value. (Uplo <> "U" nor "L") = -2: The argument Diag had an illegal value. (Diag <> "N" nor "U") = -3: The argument N had an illegal value. (N < 0) = -4: The argument Ap() is invalid. = i > 0: The i-th diagonal element of A is exactly zero. The triangular matrix is singular and its inverse can not be computed. Reference LAPACK Example Program Compute the inverse matrix of A, where ( -1.13 0 0 ) A = ( 0.26 -1.98 0 ) ( -0.96 0.30 -2.32 ) Sub Ex_Dtptri() Const N = 3 Dim Ap(N * (N + 1) / 2) As Double, Info As Long Ap(0) = -1.13 Ap(1) = 0.26: Ap(3) = -1.98 Ap(2) = -0.96: Ap(4) = 0.3: Ap(5) = -2.32 Call Dtptri("L", "N", N, Ap(), Info) Debug.Print "Inv(A) =" Debug.Print Ap(0) Debug.Print Ap(1), Ap(3) Debug.Print Ap(2), Ap(4), Ap(5) Debug.Print "Info =", Info End Sub Example Results Inv(A) = -0.884955752212389 0 0 -0.116206310896576 -0.505050505050505 0 0.35116190898919 -6.53082549634274E-02 -0.431034482758621 Info = 0