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LAPACK: Linear Algebra PACKage
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dstt21.f File Reference

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Functions/Subroutines

subroutine dstt21 (N, KBAND, AD, AE, SD, SE, U, LDU, WORK, RESULT)
 DSTT21 More...
 

Function/Subroutine Documentation

subroutine dstt21 ( integer  N,
integer  KBAND,
double precision, dimension( * )  AD,
double precision, dimension( * )  AE,
double precision, dimension( * )  SD,
double precision, dimension( * )  SE,
double precision, dimension( ldu, * )  U,
integer  LDU,
double precision, dimension( * )  WORK,
double precision, dimension( 2 )  RESULT 
)

DSTT21

Purpose:
 DSTT21 checks a decomposition of the form

    A = U S U'

 where ' means transpose, A is symmetric tridiagonal, U is orthogonal,
 and S is diagonal (if KBAND=0) or symmetric tridiagonal (if KBAND=1).
 Two tests are performed:

    RESULT(1) = | A - U S U' | / ( |A| n ulp )

    RESULT(2) = | I - UU' | / ( n ulp )
Parameters
[in]N
          N is INTEGER
          The size of the matrix.  If it is zero, DSTT21 does nothing.
          It must be at least zero.
[in]KBAND
          KBAND is INTEGER
          The bandwidth of the matrix S.  It may only be zero or one.
          If zero, then S is diagonal, and SE is not referenced.  If
          one, then S is symmetric tri-diagonal.
[in]AD
          AD is DOUBLE PRECISION array, dimension (N)
          The diagonal of the original (unfactored) matrix A.  A is
          assumed to be symmetric tridiagonal.
[in]AE
          AE is DOUBLE PRECISION array, dimension (N-1)
          The off-diagonal of the original (unfactored) matrix A.  A
          is assumed to be symmetric tridiagonal.  AE(1) is the (1,2)
          and (2,1) element, AE(2) is the (2,3) and (3,2) element, etc.
[in]SD
          SD is DOUBLE PRECISION array, dimension (N)
          The diagonal of the (symmetric tri-) diagonal matrix S.
[in]SE
          SE is DOUBLE PRECISION array, dimension (N-1)
          The off-diagonal of the (symmetric tri-) diagonal matrix S.
          Not referenced if KBSND=0.  If KBAND=1, then AE(1) is the
          (1,2) and (2,1) element, SE(2) is the (2,3) and (3,2)
          element, etc.
[in]U
          U is DOUBLE PRECISION array, dimension (LDU, N)
          The orthogonal matrix in the decomposition.
[in]LDU
          LDU is INTEGER
          The leading dimension of U.  LDU must be at least N.
[out]WORK
          WORK is DOUBLE PRECISION array, dimension (N*(N+1))
[out]RESULT
          RESULT is DOUBLE PRECISION array, dimension (2)
          The values computed by the two tests described above.  The
          values are currently limited to 1/ulp, to avoid overflow.
          RESULT(1) is always modified.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
November 2011

Definition at line 127 of file dstt21.f.

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