LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
clanhs.f
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1 *> \brief \b CLANHS returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of an upper Hessenberg matrix.
2 *
3 * =========== DOCUMENTATION ===========
4 *
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17 *
18 * Definition:
19 * ===========
20 *
21 * REAL FUNCTION CLANHS( NORM, N, A, LDA, WORK )
22 *
23 * .. Scalar Arguments ..
24 * CHARACTER NORM
25 * INTEGER LDA, N
26 * ..
27 * .. Array Arguments ..
28 * REAL WORK( * )
29 * COMPLEX A( LDA, * )
30 * ..
31 *
32 *
33 *> \par Purpose:
34 * =============
35 *>
36 *> \verbatim
37 *>
38 *> CLANHS returns the value of the one norm, or the Frobenius norm, or
39 *> the infinity norm, or the element of largest absolute value of a
40 *> Hessenberg matrix A.
41 *> \endverbatim
42 *>
43 *> \return CLANHS
44 *> \verbatim
45 *>
46 *> CLANHS = ( max(abs(A(i,j))), NORM = 'M' or 'm'
47 *> (
48 *> ( norm1(A), NORM = '1', 'O' or 'o'
49 *> (
50 *> ( normI(A), NORM = 'I' or 'i'
51 *> (
52 *> ( normF(A), NORM = 'F', 'f', 'E' or 'e'
53 *>
54 *> where norm1 denotes the one norm of a matrix (maximum column sum),
55 *> normI denotes the infinity norm of a matrix (maximum row sum) and
56 *> normF denotes the Frobenius norm of a matrix (square root of sum of
57 *> squares). Note that max(abs(A(i,j))) is not a consistent matrix norm.
58 *> \endverbatim
59 *
60 * Arguments:
61 * ==========
62 *
63 *> \param[in] NORM
64 *> \verbatim
65 *> NORM is CHARACTER*1
66 *> Specifies the value to be returned in CLANHS as described
67 *> above.
68 *> \endverbatim
69 *>
70 *> \param[in] N
71 *> \verbatim
72 *> N is INTEGER
73 *> The order of the matrix A. N >= 0. When N = 0, CLANHS is
74 *> set to zero.
75 *> \endverbatim
76 *>
77 *> \param[in] A
78 *> \verbatim
79 *> A is COMPLEX array, dimension (LDA,N)
80 *> The n by n upper Hessenberg matrix A; the part of A below the
81 *> first sub-diagonal is not referenced.
82 *> \endverbatim
83 *>
84 *> \param[in] LDA
85 *> \verbatim
86 *> LDA is INTEGER
87 *> The leading dimension of the array A. LDA >= max(N,1).
88 *> \endverbatim
89 *>
90 *> \param[out] WORK
91 *> \verbatim
92 *> WORK is REAL array, dimension (MAX(1,LWORK)),
93 *> where LWORK >= N when NORM = 'I'; otherwise, WORK is not
94 *> referenced.
95 *> \endverbatim
96 *
97 * Authors:
98 * ========
99 *
100 *> \author Univ. of Tennessee
101 *> \author Univ. of California Berkeley
102 *> \author Univ. of Colorado Denver
103 *> \author NAG Ltd.
104 *
105 *> \date September 2012
106 *
107 *> \ingroup complexOTHERauxiliary
108 *
109 * =====================================================================
110  REAL FUNCTION clanhs( NORM, N, A, LDA, WORK )
111 *
112 * -- LAPACK auxiliary routine (version 3.4.2) --
113 * -- LAPACK is a software package provided by Univ. of Tennessee, --
114 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
115 * September 2012
116 *
117 * .. Scalar Arguments ..
118  CHARACTER NORM
119  INTEGER LDA, N
120 * ..
121 * .. Array Arguments ..
122  REAL WORK( * )
123  COMPLEX A( lda, * )
124 * ..
125 *
126 * =====================================================================
127 *
128 * .. Parameters ..
129  REAL ONE, ZERO
130  parameter ( one = 1.0e+0, zero = 0.0e+0 )
131 * ..
132 * .. Local Scalars ..
133  INTEGER I, J
134  REAL SCALE, SUM, VALUE
135 * ..
136 * .. External Functions ..
137  LOGICAL LSAME, SISNAN
138  EXTERNAL lsame, sisnan
139 * ..
140 * .. External Subroutines ..
141  EXTERNAL classq
142 * ..
143 * .. Intrinsic Functions ..
144  INTRINSIC abs, min, sqrt
145 * ..
146 * .. Executable Statements ..
147 *
148  IF( n.EQ.0 ) THEN
149  VALUE = zero
150  ELSE IF( lsame( norm, 'M' ) ) THEN
151 *
152 * Find max(abs(A(i,j))).
153 *
154  VALUE = zero
155  DO 20 j = 1, n
156  DO 10 i = 1, min( n, j+1 )
157  sum = abs( a( i, j ) )
158  IF( VALUE .LT. sum .OR. sisnan( sum ) ) VALUE = sum
159  10 CONTINUE
160  20 CONTINUE
161  ELSE IF( ( lsame( norm, 'O' ) ) .OR. ( norm.EQ.'1' ) ) THEN
162 *
163 * Find norm1(A).
164 *
165  VALUE = zero
166  DO 40 j = 1, n
167  sum = zero
168  DO 30 i = 1, min( n, j+1 )
169  sum = sum + abs( a( i, j ) )
170  30 CONTINUE
171  IF( VALUE .LT. sum .OR. sisnan( sum ) ) VALUE = sum
172  40 CONTINUE
173  ELSE IF( lsame( norm, 'I' ) ) THEN
174 *
175 * Find normI(A).
176 *
177  DO 50 i = 1, n
178  work( i ) = zero
179  50 CONTINUE
180  DO 70 j = 1, n
181  DO 60 i = 1, min( n, j+1 )
182  work( i ) = work( i ) + abs( a( i, j ) )
183  60 CONTINUE
184  70 CONTINUE
185  VALUE = zero
186  DO 80 i = 1, n
187  sum = work( i )
188  IF( VALUE .LT. sum .OR. sisnan( sum ) ) VALUE = sum
189  80 CONTINUE
190  ELSE IF( ( lsame( norm, 'F' ) ) .OR. ( lsame( norm, 'E' ) ) ) THEN
191 *
192 * Find normF(A).
193 *
194  scale = zero
195  sum = one
196  DO 90 j = 1, n
197  CALL classq( min( n, j+1 ), a( 1, j ), 1, scale, sum )
198  90 CONTINUE
199  VALUE = scale*sqrt( sum )
200  END IF
201 *
202  clanhs = VALUE
203  RETURN
204 *
205 * End of CLANHS
206 *
207  END
subroutine classq(N, X, INCX, SCALE, SUMSQ)
CLASSQ updates a sum of squares represented in scaled form.
Definition: classq.f:108
real function clanhs(NORM, N, A, LDA, WORK)
CLANHS returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value ...
Definition: clanhs.f:111