101 REAL FUNCTION slanst( NORM, N, D, E )
120 parameter ( one = 1.0e+0, zero = 0.0e+0 )
124 REAL ANORM, SCALE, SUM
127 LOGICAL LSAME, SISNAN
128 EXTERNAL lsame, sisnan
140 ELSE IF( lsame( norm,
'M' ) )
THEN
144 anorm = abs( d( n ) )
147 IF( anorm .LT. sum .OR. sisnan( sum ) ) anorm = sum
149 IF( anorm .LT. sum .OR. sisnan( sum ) ) anorm = sum
151 ELSE IF( lsame( norm,
'O' ) .OR. norm.EQ.
'1' .OR.
152 $ lsame( norm,
'I' ) )
THEN
157 anorm = abs( d( 1 ) )
159 anorm = abs( d( 1 ) )+abs( e( 1 ) )
160 sum = abs( e( n-1 ) )+abs( d( n ) )
161 IF( anorm .LT. sum .OR. sisnan( sum ) ) anorm = sum
163 sum = abs( d( i ) )+abs( e( i ) )+abs( e( i-1 ) )
164 IF( anorm .LT. sum .OR. sisnan( sum ) ) anorm = sum
167 ELSE IF( ( lsame( norm,
'F' ) ) .OR. ( lsame( norm,
'E' ) ) )
THEN
174 CALL slassq( n-1, e, 1, scale, sum )
177 CALL slassq( n, d, 1, scale, sum )
178 anorm = scale*sqrt( sum )
real function slanst(NORM, N, D, E)
SLANST 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.
subroutine slassq(N, X, INCX, SCALE, SUMSQ)
SLASSQ updates a sum of squares represented in scaled form.