.TH "TESTING/EIG/cstt21.f" 3 "Version 3.12.0" "LAPACK" \" -*- nroff -*-
.ad l
.nh
.SH NAME
TESTING/EIG/cstt21.f
.SH SYNOPSIS
.br
.PP
.SS "Functions/Subroutines"

.in +1c
.ti -1c
.RI "subroutine \fBcstt21\fP (n, kband, ad, ae, sd, se, u, ldu, work, rwork, result)"
.br
.RI "\fBCSTT21\fP "
.in -1c
.SH "Function/Subroutine Documentation"
.PP 
.SS "subroutine cstt21 (integer n, integer kband, real, dimension( * ) ad, real, dimension( * ) ae, real, dimension( * ) sd, real, dimension( * ) se, complex, dimension( ldu, * ) u, integer ldu, complex, dimension( * ) work, real, dimension( * ) rwork, real, dimension( 2 ) result)"

.PP
\fBCSTT21\fP 
.PP
\fBPurpose:\fP
.RS 4

.PP
.nf
 CSTT21  checks a decomposition of the form

    A = U S U**H

 where **H means conjugate transpose, A is real symmetric tridiagonal,
 U is unitary, and S is real and diagonal (if KBAND=0) or symmetric
 tridiagonal (if KBAND=1)\&.  Two tests are performed:

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

    RESULT(2) = | I - U U**H | / ( n ulp )
.fi
.PP
 
.RE
.PP
\fBParameters\fP
.RS 4
\fIN\fP 
.PP
.nf
          N is INTEGER
          The size of the matrix\&.  If it is zero, CSTT21 does nothing\&.
          It must be at least zero\&.
.fi
.PP
.br
\fIKBAND\fP 
.PP
.nf
          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\&.
.fi
.PP
.br
\fIAD\fP 
.PP
.nf
          AD is REAL array, dimension (N)
          The diagonal of the original (unfactored) matrix A\&.  A is
          assumed to be real symmetric tridiagonal\&.
.fi
.PP
.br
\fIAE\fP 
.PP
.nf
          AE is REAL 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\&.
.fi
.PP
.br
\fISD\fP 
.PP
.nf
          SD is REAL array, dimension (N)
          The diagonal of the real (symmetric tri-) diagonal matrix S\&.
.fi
.PP
.br
\fISE\fP 
.PP
.nf
          SE is REAL 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\&.
.fi
.PP
.br
\fIU\fP 
.PP
.nf
          U is COMPLEX array, dimension (LDU, N)
          The unitary matrix in the decomposition\&.
.fi
.PP
.br
\fILDU\fP 
.PP
.nf
          LDU is INTEGER
          The leading dimension of U\&.  LDU must be at least N\&.
.fi
.PP
.br
\fIWORK\fP 
.PP
.nf
          WORK is COMPLEX array, dimension (N**2)
.fi
.PP
.br
\fIRWORK\fP 
.PP
.nf
          RWORK is REAL array, dimension (N)
.fi
.PP
.br
\fIRESULT\fP 
.PP
.nf
          RESULT is REAL 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\&.
.fi
.PP
 
.RE
.PP
\fBAuthor\fP
.RS 4
Univ\&. of Tennessee 
.PP
Univ\&. of California Berkeley 
.PP
Univ\&. of Colorado Denver 
.PP
NAG Ltd\&. 
.RE
.PP

.PP
Definition at line \fB131\fP of file \fBcstt21\&.f\fP\&.
.SH "Author"
.PP 
Generated automatically by Doxygen for LAPACK from the source code\&.