WDgbsv WDgesv WDgtsv WDtrtrs

WDgtsv() Function WDgtsv ( N As  Long, Dl As  Variant, D As  Variant, Du As  Variant, B As  Variant, Optional Nrhs As  Long = 1  ) Solution to system of linear equations AX = B for a general tridiagonal matrix Purpose WDgtsv solves the equation A * X = B where A is an N x N tridiagonal matrix, by Gaussian elimination with partial pivoting. Note that the equation A^T*X = B may be solved by interchanging the order of the arguments Du and Dl. Returns N+2 x Nrhs Column 1 Column 2 . . . Column Nrhs Rows 1 to N Solution matrix X Row N+1 Reciprocal condition number 0 . . . 0 Row N+2 Return code 0 . . . 0 Return code. = 0: Successful exit. = i > 0: The i-th diagonal element of the factor is zero. (Matrix A is singular) Parameters [in] N Number of linear equations, i.e., order of the matrix A. (N >= 1) [in] Dl (N-1) Sub-diagonal elements of coefficient matrix A. [in] D (N) Diagonal elements of coefficient matrix A. [in] Du (N-1) Super-diagonal elements of coefficient matrix A. [in] B (N x Nrhs) N x Nrhs right hand side matrix B. [in] Nrhs (Optional) Number of columns of right hand side matrix B. (Nrhs >= 1) (default = 1) Reference LAPACK Example Solve the system of linear equations Ax = B and estimate the reciprocal of the condition number (RCond) of A, where A is a tridiagonal matrix and ( -0.58 1.14 0 ) ( -0.5960 ) A = ( -1.56 2.21 0.16 ), B = ( -0.6798 ) ( 0 0.24 0.25 ) ( -0.0406 )