Dpbcon Dpbtrf Dpbtrs Dptcon Dpttrf Dpttrs

Dptcon() Sub Dptcon ( N As  Long, D() As  Double, E() As  Double, ANorm As  Double, RCond As  Double, Info As  Long  ) 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 / (norm(A) * norm(inv(A))). Parameters [in] N Order of the matrix A. (N >= 0) (If N = 0, returns RCond = 1) [in] D() Array D(LD - 1) (LD >= N) N diagonal elements of the diagonal matrix D from the factorization of A, as computed by Dpttrf. [in] E() Array E(LE - 1) (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 the1-norm of inv(A) computed in this routine. [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 ANorm had an illegal value. (ANorm < 0) Reference LAPACK Example Program See example of Dptsv.