Dtbcon Dtbtrs Dtpcon Dtptri Dtptrs Dtrcon Dtrtri Dtrtrs

Dtrtri() Sub Dtrtri ( Uplo As  String, Diag As  String, N As  Long, A() As  Double, Info As  Long  ) Inverse of a triangular matrix Purpose This routine computes the inverse of a real upper or lower triangular matrix A. This is the Level 3 BLAS version of the algorithm. 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 A() 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] A() Array A(LA1 - 1, LA2 - 1) (LA1 >= N, LA2 >= N) [in] N x N triangular matrix A. Only the upper or lower triangular part is to be referenced in accordance with Uplo. [out] The (triangular) inverse of the original matrix. [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 A() 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_Dtrtri() Const N = 3 Dim A(N - 1, N - 1) As Double, Info As Long A(0, 0) = -1.13 A(1, 0) = 0.26: A(1, 1) = -1.98 A(2, 0) = -0.96: A(2, 1) = 0.3: A(2, 2) = -2.32 Call Dtrtri("L", "N", N, A(), Info) Debug.Print "Inv(A) =" Debug.Print A(0, 0), A(0, 1), A(0, 2) Debug.Print A(1, 0), A(1, 1), A(1, 2) Debug.Print A(2, 0), A(2, 1), A(2, 2) 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