dpbcon dpbtrf dpbtrs dptcon dpttrf dpttrs

dptcon() void dptcon ( int  n, double  d[], double  e[], double  anorm, double *  rcond, double  work[], int *  info  ) Condition number of a symmetric positive definite tridiagonal matrix Purpose This routine computes the reciprocal of the condition number (in the 1-norm) of a real symmetric positive definite tridiagonal matrix using the factorization A = L*D*L^T or A = U^T*D*U computed by dpttrf. Norm(inv(A)) is computed by a direct method, and the reciprocal of the condition number is computed as rcond = 1 / (anorm * norm(inv(A))). Parameters [in] n Order of the matrix A. (n >= 0) (If n = 0, returns rcond = 1) [in] d[] Array d[ld] (ld >= n) n diagonal elements of the diagonal matrix D from the factorization of A, as computed by dpttrf. [in] e[] Array e[le] (le >= n - 1) n-1 sub-diagonal elements of the unit bidiagonal factor U or L from the factorization of A, as computed by dpttrf. [in] anorm The 1-norm of the original matrix A. (anorm >= 0) [out] rcond The reciprocal of the condition number of the matrix A, computed as rcond = 1/(anorm * ainvnm), where ainvnm is the 1-norm of inv(A) computed in this routine. [out] work[] Array work[lwork] (lwork >= n) Work array. [out] info = 0: Successful exit = -1: The argument n had an illegal value (n < 0) = -4: The argument anorm had an illegal value (anorm < 0) Reference LAPACK