 LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
 double precision function dlanst ( character NORM, integer N, double precision, dimension( * ) D, double precision, dimension( * ) E )

DLANST returns the value of the 1-norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real symmetric tridiagonal matrix.

Purpose:
``` DLANST  returns the value of the one norm,  or the Frobenius norm, or
the  infinity norm,  or the  element of  largest absolute value  of a
real symmetric tridiagonal matrix A.```
Returns
DLANST
```    DLANST = ( max(abs(A(i,j))), NORM = 'M' or 'm'
(
( norm1(A),         NORM = '1', 'O' or 'o'
(
( normI(A),         NORM = 'I' or 'i'
(
( normF(A),         NORM = 'F', 'f', 'E' or 'e'

where  norm1  denotes the  one norm of a matrix (maximum column sum),
normI  denotes the  infinity norm  of a matrix  (maximum row sum) and
normF  denotes the  Frobenius norm of a matrix (square root of sum of
squares).  Note that  max(abs(A(i,j)))  is not a consistent matrix norm.```
Parameters
 [in] NORM ``` NORM is CHARACTER*1 Specifies the value to be returned in DLANST as described above.``` [in] N ``` N is INTEGER The order of the matrix A. N >= 0. When N = 0, DLANST is set to zero.``` [in] D ``` D is DOUBLE PRECISION array, dimension (N) The diagonal elements of A.``` [in] E ``` E is DOUBLE PRECISION array, dimension (N-1) The (n-1) sub-diagonal or super-diagonal elements of A.```
Date
September 2012

Definition at line 102 of file dlanst.f.

102 *
103 * -- LAPACK auxiliary routine (version 3.4.2) --
104 * -- LAPACK is a software package provided by Univ. of Tennessee, --
105 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
106 * September 2012
107 *
108 * .. Scalar Arguments ..
109  CHARACTER norm
110  INTEGER n
111 * ..
112 * .. Array Arguments ..
113  DOUBLE PRECISION d( * ), e( * )
114 * ..
115 *
116 * =====================================================================
117 *
118 * .. Parameters ..
119  DOUBLE PRECISION one, zero
120  parameter ( one = 1.0d+0, zero = 0.0d+0 )
121 * ..
122 * .. Local Scalars ..
123  INTEGER i
124  DOUBLE PRECISION anorm, scale, sum
125 * ..
126 * .. External Functions ..
127  LOGICAL lsame, disnan
128  EXTERNAL lsame, disnan
129 * ..
130 * .. External Subroutines ..
131  EXTERNAL dlassq
132 * ..
133 * .. Intrinsic Functions ..
134  INTRINSIC abs, sqrt
135 * ..
136 * .. Executable Statements ..
137 *
138  IF( n.LE.0 ) THEN
139  anorm = zero
140  ELSE IF( lsame( norm, 'M' ) ) THEN
141 *
142 * Find max(abs(A(i,j))).
143 *
144  anorm = abs( d( n ) )
145  DO 10 i = 1, n - 1
146  sum = abs( d( i ) )
147  IF( anorm .LT. sum .OR. disnan( sum ) ) anorm = sum
148  sum = abs( e( i ) )
149  IF( anorm .LT. sum .OR. disnan( sum ) ) anorm = sum
150  10 CONTINUE
151  ELSE IF( lsame( norm, 'O' ) .OR. norm.EQ.'1' .OR.
152  \$ lsame( norm, 'I' ) ) THEN
153 *
154 * Find norm1(A).
155 *
156  IF( n.EQ.1 ) THEN
157  anorm = abs( d( 1 ) )
158  ELSE
159  anorm = abs( d( 1 ) )+abs( e( 1 ) )
160  sum = abs( e( n-1 ) )+abs( d( n ) )
161  IF( anorm .LT. sum .OR. disnan( sum ) ) anorm = sum
162  DO 20 i = 2, n - 1
163  sum = abs( d( i ) )+abs( e( i ) )+abs( e( i-1 ) )
164  IF( anorm .LT. sum .OR. disnan( sum ) ) anorm = sum
165  20 CONTINUE
166  END IF
167  ELSE IF( ( lsame( norm, 'F' ) ) .OR. ( lsame( norm, 'E' ) ) ) THEN
168 *
169 * Find normF(A).
170 *
171  scale = zero
172  sum = one
173  IF( n.GT.1 ) THEN
174  CALL dlassq( n-1, e, 1, scale, sum )
175  sum = 2*sum
176  END IF
177  CALL dlassq( n, d, 1, scale, sum )
178  anorm = scale*sqrt( sum )
179  END IF
180 *
181  dlanst = anorm
182  RETURN
183 *
184 * End of DLANST
185 *
logical function disnan(DIN)
DISNAN tests input for NaN.
Definition: disnan.f:61
subroutine dlassq(N, X, INCX, SCALE, SUMSQ)
DLASSQ updates a sum of squares represented in scaled form.
Definition: dlassq.f:105
double precision function dlanst(NORM, N, D, E)
DLANST returns the value of the 1-norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real symmetric tridiagonal matrix.
Definition: dlanst.f:102
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:55

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