.TH "TESTING/EIG/zstt21.f" 3 "Version 3.12.0" "LAPACK" \" -*- nroff -*- .ad l .nh .SH NAME TESTING/EIG/zstt21.f .SH SYNOPSIS .br .PP .SS "Functions/Subroutines" .in +1c .ti -1c .RI "subroutine \fBzstt21\fP (n, kband, ad, ae, sd, se, u, ldu, work, rwork, result)" .br .RI "\fBZSTT21\fP " .in -1c .SH "Function/Subroutine Documentation" .PP .SS "subroutine zstt21 (integer n, integer kband, double precision, dimension( * ) ad, double precision, dimension( * ) ae, double precision, dimension( * ) sd, double precision, dimension( * ) se, complex*16, dimension( ldu, * ) u, integer ldu, complex*16, dimension( * ) work, double precision, dimension( * ) rwork, double precision, dimension( 2 ) result)" .PP \fBZSTT21\fP .PP \fBPurpose:\fP .RS 4 .PP .nf !> !> ZSTT21 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, ZSTT21 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 DOUBLE PRECISION 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 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\&. !> .fi .PP .br \fISD\fP .PP .nf !> SD is DOUBLE PRECISION array, dimension (N) !> The diagonal of the real (symmetric tri-) diagonal matrix S\&. !> .fi .PP .br \fISE\fP .PP .nf !> 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\&. !> .fi .PP .br \fIU\fP .PP .nf !> U is COMPLEX*16 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*16 array, dimension (N**2) !> .fi .PP .br \fIRWORK\fP .PP .nf !> RWORK is DOUBLE PRECISION array, dimension (N) !> .fi .PP .br \fIRESULT\fP .PP .nf !> 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\&. !> .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 \fBzstt21\&.f\fP\&. .SH "Author" .PP Generated automatically by Doxygen for LAPACK from the source code\&.