Dpbcon Dpbtrf Dpbtrs Dptcon Dpttrf Dpttrs

Dpttrs() Sub Dpttrs ( N As  Long, D() As  Double, E() As  Double, B() As  Double, Info As  Long, Optional Nrhs As  Long = 1  ) Solution to factorized system of linear equations AX = B for a symmetric positive definite tridiagonal matrix Purpose This routine solves a symmetric positive definite tridiagonal system of the form A * X = B using the L*D*L^T factorization of A computed by Dpttrf. D is a diagonal matrix specified in the vector D, L is a unit bidiagonal matrix whose sub-diagonal is specified in the vector E, and X and B are n x nrhs matrices. Parameters [in] N Order of the matrix A. (N >= 0) (If N = 0, returns without computation) [in] D() Array D(LD - 1) (LD >= N) N diagonal elements of the diagonal matrix D from the L*D*L^T factorization of A. [in] E() Array E(LE - 1) (LE >= N - 1) N-1 sub-diagonal elements of the unit bidiagonal factor L from the L*D*L^T factorization of A. E can also be regarded as the super-diagonal of the unit bidiagonal factor U from the U^T*D*U factorization of A. [in,out] B() Array B(LB1 - 1, LB2 - 1) (LB1 >= max(1, N), LB2 >= Nrhs) (2D array) or B(LB - 1) (LB >= max(1, N), Nrhs = 1) (1D array) [in] N x Nrhs right hand side matrix B. [out] If Info = 0, the N x Nrhs solution matrix X. [out] Info = 0: Successful exit. = -1: The argument N had an illegal value. (N < 0) = -2: The argument D() is invalid. = -3: The argument E() is invalid. = -4: The argument B() is invalid. = -6: The argument Nrhs had an illegal value. (Nrhs < 0) [in] Nrhs (Optional) Number of right hand sides, i.e., number of columns of the matrix B. (Nrhs >= 0) (If Nrhs = 0, returns without computation) (default = 1) Reference LAPACK Example Program See example of Dpttrf.