LAPACK 3.11.0
LAPACK: Linear Algebra PACKage

◆ dgtt01()

subroutine dgtt01 ( integer  N,
double precision, dimension( * )  DL,
double precision, dimension( * )  D,
double precision, dimension( * )  DU,
double precision, dimension( * )  DLF,
double precision, dimension( * )  DF,
double precision, dimension( * )  DUF,
double precision, dimension( * )  DU2,
integer, dimension( * )  IPIV,
double precision, dimension( ldwork, * )  WORK,
integer  LDWORK,
double precision, dimension( * )  RWORK,
double precision  RESID 
)

DGTT01

Purpose:
 DGTT01 reconstructs a tridiagonal matrix A from its LU factorization
 and computes the residual
    norm(L*U - A) / ( norm(A) * EPS ),
 where EPS is the machine epsilon.
Parameters
[in]N
          N is INTEGTER
          The order of the matrix A.  N >= 0.
[in]DL
          DL is DOUBLE PRECISION array, dimension (N-1)
          The (n-1) sub-diagonal elements of A.
[in]D
          D is DOUBLE PRECISION array, dimension (N)
          The diagonal elements of A.
[in]DU
          DU is DOUBLE PRECISION array, dimension (N-1)
          The (n-1) super-diagonal elements of A.
[in]DLF
          DLF is DOUBLE PRECISION array, dimension (N-1)
          The (n-1) multipliers that define the matrix L from the
          LU factorization of A.
[in]DF
          DF is DOUBLE PRECISION array, dimension (N)
          The n diagonal elements of the upper triangular matrix U from
          the LU factorization of A.
[in]DUF
          DUF is DOUBLE PRECISION array, dimension (N-1)
          The (n-1) elements of the first super-diagonal of U.
[in]DU2
          DU2 is DOUBLE PRECISION array, dimension (N-2)
          The (n-2) elements of the second super-diagonal of U.
[in]IPIV
          IPIV is INTEGER array, dimension (N)
          The pivot indices; for 1 <= i <= n, row i of the matrix was
          interchanged with row IPIV(i).  IPIV(i) will always be either
          i or i+1; IPIV(i) = i indicates a row interchange was not
          required.
[out]WORK
          WORK is DOUBLE PRECISION array, dimension (LDWORK,N)
[in]LDWORK
          LDWORK is INTEGER
          The leading dimension of the array WORK.  LDWORK >= max(1,N).
[out]RWORK
          RWORK is DOUBLE PRECISION array, dimension (N)
[out]RESID
          RESID is DOUBLE PRECISION
          The scaled residual:  norm(L*U - A) / (norm(A) * EPS)
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.