LAPACK  3.10.0
LAPACK: Linear Algebra PACKage
zstt21.f
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1 *> \brief \b ZSTT21
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 * Definition:
9 * ===========
10 *
11 * SUBROUTINE ZSTT21( N, KBAND, AD, AE, SD, SE, U, LDU, WORK, RWORK,
12 * RESULT )
13 *
14 * .. Scalar Arguments ..
15 * INTEGER KBAND, LDU, N
16 * ..
17 * .. Array Arguments ..
18 * DOUBLE PRECISION AD( * ), AE( * ), RESULT( 2 ), RWORK( * ),
19 * $ SD( * ), SE( * )
20 * COMPLEX*16 U( LDU, * ), WORK( * )
21 * ..
22 *
23 *
24 *> \par Purpose:
25 * =============
26 *>
27 *> \verbatim
28 *>
29 *> ZSTT21 checks a decomposition of the form
30 *>
31 *> A = U S U**H
32 *>
33 *> where **H means conjugate transpose, A is real symmetric tridiagonal,
34 *> U is unitary, and S is real and diagonal (if KBAND=0) or symmetric
35 *> tridiagonal (if KBAND=1). Two tests are performed:
36 *>
37 *> RESULT(1) = | A - U S U**H | / ( |A| n ulp )
38 *>
39 *> RESULT(2) = | I - U U**H | / ( n ulp )
40 *> \endverbatim
41 *
42 * Arguments:
43 * ==========
44 *
45 *> \param[in] N
46 *> \verbatim
47 *> N is INTEGER
48 *> The size of the matrix. If it is zero, ZSTT21 does nothing.
49 *> It must be at least zero.
50 *> \endverbatim
51 *>
52 *> \param[in] KBAND
53 *> \verbatim
54 *> KBAND is INTEGER
55 *> The bandwidth of the matrix S. It may only be zero or one.
56 *> If zero, then S is diagonal, and SE is not referenced. If
57 *> one, then S is symmetric tri-diagonal.
58 *> \endverbatim
59 *>
60 *> \param[in] AD
61 *> \verbatim
62 *> AD is DOUBLE PRECISION array, dimension (N)
63 *> The diagonal of the original (unfactored) matrix A. A is
64 *> assumed to be real symmetric tridiagonal.
65 *> \endverbatim
66 *>
67 *> \param[in] AE
68 *> \verbatim
69 *> AE is DOUBLE PRECISION array, dimension (N-1)
70 *> The off-diagonal of the original (unfactored) matrix A. A
71 *> is assumed to be symmetric tridiagonal. AE(1) is the (1,2)
72 *> and (2,1) element, AE(2) is the (2,3) and (3,2) element, etc.
73 *> \endverbatim
74 *>
75 *> \param[in] SD
76 *> \verbatim
77 *> SD is DOUBLE PRECISION array, dimension (N)
78 *> The diagonal of the real (symmetric tri-) diagonal matrix S.
79 *> \endverbatim
80 *>
81 *> \param[in] SE
82 *> \verbatim
83 *> SE is DOUBLE PRECISION array, dimension (N-1)
84 *> The off-diagonal of the (symmetric tri-) diagonal matrix S.
85 *> Not referenced if KBSND=0. If KBAND=1, then AE(1) is the
86 *> (1,2) and (2,1) element, SE(2) is the (2,3) and (3,2)
87 *> element, etc.
88 *> \endverbatim
89 *>
90 *> \param[in] U
91 *> \verbatim
92 *> U is COMPLEX*16 array, dimension (LDU, N)
93 *> The unitary matrix in the decomposition.
94 *> \endverbatim
95 *>
96 *> \param[in] LDU
97 *> \verbatim
98 *> LDU is INTEGER
99 *> The leading dimension of U. LDU must be at least N.
100 *> \endverbatim
101 *>
102 *> \param[out] WORK
103 *> \verbatim
104 *> WORK is COMPLEX*16 array, dimension (N**2)
105 *> \endverbatim
106 *>
107 *> \param[out] RWORK
108 *> \verbatim
109 *> RWORK is DOUBLE PRECISION array, dimension (N)
110 *> \endverbatim
111 *>
112 *> \param[out] RESULT
113 *> \verbatim
114 *> RESULT is DOUBLE PRECISION array, dimension (2)
115 *> The values computed by the two tests described above. The
116 *> values are currently limited to 1/ulp, to avoid overflow.
117 *> RESULT(1) is always modified.
118 *> \endverbatim
119 *
120 * Authors:
121 * ========
122 *
123 *> \author Univ. of Tennessee
124 *> \author Univ. of California Berkeley
125 *> \author Univ. of Colorado Denver
126 *> \author NAG Ltd.
127 *
128 *> \ingroup complex16_eig
129 *
130 * =====================================================================
131  SUBROUTINE zstt21( N, KBAND, AD, AE, SD, SE, U, LDU, WORK, RWORK,
132  $ RESULT )
133 *
134 * -- LAPACK test routine --
135 * -- LAPACK is a software package provided by Univ. of Tennessee, --
136 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
137 *
138 * .. Scalar Arguments ..
139  INTEGER KBAND, LDU, N
140 * ..
141 * .. Array Arguments ..
142  DOUBLE PRECISION AD( * ), AE( * ), RESULT( 2 ), RWORK( * ),
143  $ sd( * ), se( * )
144  COMPLEX*16 U( LDU, * ), WORK( * )
145 * ..
146 *
147 * =====================================================================
148 *
149 * .. Parameters ..
150  DOUBLE PRECISION ZERO, ONE
151  parameter( zero = 0.0d+0, one = 1.0d+0 )
152  COMPLEX*16 CZERO, CONE
153  parameter( czero = ( 0.0d+0, 0.0d+0 ),
154  $ cone = ( 1.0d+0, 0.0d+0 ) )
155 * ..
156 * .. Local Scalars ..
157  INTEGER J
158  DOUBLE PRECISION ANORM, TEMP1, TEMP2, ULP, UNFL, WNORM
159 * ..
160 * .. External Functions ..
161  DOUBLE PRECISION DLAMCH, ZLANGE, ZLANHE
162  EXTERNAL dlamch, zlange, zlanhe
163 * ..
164 * .. External Subroutines ..
165  EXTERNAL zgemm, zher, zher2, zlaset
166 * ..
167 * .. Intrinsic Functions ..
168  INTRINSIC abs, dble, dcmplx, max, min
169 * ..
170 * .. Executable Statements ..
171 *
172 * 1) Constants
173 *
174  result( 1 ) = zero
175  result( 2 ) = zero
176  IF( n.LE.0 )
177  $ RETURN
178 *
179  unfl = dlamch( 'Safe minimum' )
180  ulp = dlamch( 'Precision' )
181 *
182 * Do Test 1
183 *
184 * Copy A & Compute its 1-Norm:
185 *
186  CALL zlaset( 'Full', n, n, czero, czero, work, n )
187 *
188  anorm = zero
189  temp1 = zero
190 *
191  DO 10 j = 1, n - 1
192  work( ( n+1 )*( j-1 )+1 ) = ad( j )
193  work( ( n+1 )*( j-1 )+2 ) = ae( j )
194  temp2 = abs( ae( j ) )
195  anorm = max( anorm, abs( ad( j ) )+temp1+temp2 )
196  temp1 = temp2
197  10 CONTINUE
198 *
199  work( n**2 ) = ad( n )
200  anorm = max( anorm, abs( ad( n ) )+temp1, unfl )
201 *
202 * Norm of A - USU*
203 *
204  DO 20 j = 1, n
205  CALL zher( 'L', n, -sd( j ), u( 1, j ), 1, work, n )
206  20 CONTINUE
207 *
208  IF( n.GT.1 .AND. kband.EQ.1 ) THEN
209  DO 30 j = 1, n - 1
210  CALL zher2( 'L', n, -dcmplx( se( j ) ), u( 1, j ), 1,
211  $ u( 1, j+1 ), 1, work, n )
212  30 CONTINUE
213  END IF
214 *
215  wnorm = zlanhe( '1', 'L', n, work, n, rwork )
216 *
217  IF( anorm.GT.wnorm ) THEN
218  result( 1 ) = ( wnorm / anorm ) / ( n*ulp )
219  ELSE
220  IF( anorm.LT.one ) THEN
221  result( 1 ) = ( min( wnorm, n*anorm ) / anorm ) / ( n*ulp )
222  ELSE
223  result( 1 ) = min( wnorm / anorm, dble( n ) ) / ( n*ulp )
224  END IF
225  END IF
226 *
227 * Do Test 2
228 *
229 * Compute U U**H - I
230 *
231  CALL zgemm( 'N', 'C', n, n, n, cone, u, ldu, u, ldu, czero, work,
232  $ n )
233 *
234  DO 40 j = 1, n
235  work( ( n+1 )*( j-1 )+1 ) = work( ( n+1 )*( j-1 )+1 ) - cone
236  40 CONTINUE
237 *
238  result( 2 ) = min( dble( n ), zlange( '1', n, n, work, n,
239  $ rwork ) ) / ( n*ulp )
240 *
241  RETURN
242 *
243 * End of ZSTT21
244 *
245  END
subroutine zher(UPLO, N, ALPHA, X, INCX, A, LDA)
ZHER
Definition: zher.f:135
subroutine zher2(UPLO, N, ALPHA, X, INCX, Y, INCY, A, LDA)
ZHER2
Definition: zher2.f:150
subroutine zgemm(TRANSA, TRANSB, M, N, K, ALPHA, A, LDA, B, LDB, BETA, C, LDC)
ZGEMM
Definition: zgemm.f:187
subroutine zstt21(N, KBAND, AD, AE, SD, SE, U, LDU, WORK, RWORK, RESULT)
ZSTT21
Definition: zstt21.f:133
subroutine zlaset(UPLO, M, N, ALPHA, BETA, A, LDA)
ZLASET initializes the off-diagonal elements and the diagonal elements of a matrix to given values.
Definition: zlaset.f:106