zptt02()

subroutine zptt02	(	character	UPLO,
		integer	N,
		integer	NRHS,
		double precision, dimension( * )	D,
		complex*16, dimension( * )	E,
		complex*16, dimension( ldx, * )	X,
		integer	LDX,
		complex*16, dimension( ldb, * )	B,
		integer	LDB,
		double precision	RESID
	)

ZPTT02

Purpose:

 ZPTT02 computes the residual for the solution to a symmetric
 tridiagonal system of equations:
    RESID = norm(B - A*X) / (norm(A) * norm(X) * EPS),
 where EPS is the machine epsilon.

Parameters

[in]	UPLO	UPLO is CHARACTER*1 Specifies whether the superdiagonal or the subdiagonal of the tridiagonal matrix A is stored. = 'U': E is the superdiagonal of A = 'L': E is the subdiagonal of A
[in]	N	N is INTEGTER The order of the matrix A.
[in]	NRHS	NRHS is INTEGER The number of right hand sides, i.e., the number of columns of the matrices B and X. NRHS >= 0.
[in]	D	D is DOUBLE PRECISION array, dimension (N) The n diagonal elements of the tridiagonal matrix A.
[in]	E	E is COMPLEX*16 array, dimension (N-1) The (n-1) subdiagonal elements of the tridiagonal matrix A.
[in]	X	X is COMPLEX*16 array, dimension (LDX,NRHS) The n by nrhs matrix of solution vectors X.
[in]	LDX	LDX is INTEGER The leading dimension of the array X. LDX >= max(1,N).
[in,out]	B	B is COMPLEX*16 array, dimension (LDB,NRHS) On entry, the n by nrhs matrix of right hand side vectors B. On exit, B is overwritten with the difference B - A*X.
[in]	LDB	LDB is INTEGER The leading dimension of the array B. LDB >= max(1,N).
[out]	RESID	RESID is DOUBLE PRECISION norm(B - A*X) / (norm(A) * norm(X) * EPS)

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.