LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
 subroutine zdrscl ( integer N, double precision SA, complex*16, dimension( * ) SX, integer INCX )

ZDRSCL multiplies a vector by the reciprocal of a real scalar.

Purpose:
``` ZDRSCL multiplies an n-element complex vector x by the real scalar
1/a.  This is done without overflow or underflow as long as
the final result x/a does not overflow or underflow.```
Parameters
 [in] N ``` N is INTEGER The number of components of the vector x.``` [in] SA ``` SA is DOUBLE PRECISION The scalar a which is used to divide each component of x. SA must be >= 0, or the subroutine will divide by zero.``` [in,out] SX ``` SX is COMPLEX*16 array, dimension (1+(N-1)*abs(INCX)) The n-element vector x.``` [in] INCX ``` INCX is INTEGER The increment between successive values of the vector SX. > 0: SX(1) = X(1) and SX(1+(i-1)*INCX) = x(i), 1< i<= n```
Date
September 2012

Definition at line 86 of file zdrscl.f.

86 *
87 * -- LAPACK auxiliary routine (version 3.4.2) --
88 * -- LAPACK is a software package provided by Univ. of Tennessee, --
89 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
90 * September 2012
91 *
92 * .. Scalar Arguments ..
93  INTEGER incx, n
94  DOUBLE PRECISION sa
95 * ..
96 * .. Array Arguments ..
97  COMPLEX*16 sx( * )
98 * ..
99 *
100 * =====================================================================
101 *
102 * .. Parameters ..
103  DOUBLE PRECISION zero, one
104  parameter ( zero = 0.0d+0, one = 1.0d+0 )
105 * ..
106 * .. Local Scalars ..
107  LOGICAL done
108  DOUBLE PRECISION bignum, cden, cden1, cnum, cnum1, mul, smlnum
109 * ..
110 * .. External Functions ..
111  DOUBLE PRECISION dlamch
112  EXTERNAL dlamch
113 * ..
114 * .. External Subroutines ..
116 * ..
117 * .. Intrinsic Functions ..
118  INTRINSIC abs
119 * ..
120 * .. Executable Statements ..
121 *
122 * Quick return if possible
123 *
124  IF( n.LE.0 )
125  \$ RETURN
126 *
127 * Get machine parameters
128 *
129  smlnum = dlamch( 'S' )
130  bignum = one / smlnum
131  CALL dlabad( smlnum, bignum )
132 *
133 * Initialize the denominator to SA and the numerator to 1.
134 *
135  cden = sa
136  cnum = one
137 *
138  10 CONTINUE
139  cden1 = cden*smlnum
140  cnum1 = cnum / bignum
141  IF( abs( cden1 ).GT.abs( cnum ) .AND. cnum.NE.zero ) THEN
142 *
143 * Pre-multiply X by SMLNUM if CDEN is large compared to CNUM.
144 *
145  mul = smlnum
146  done = .false.
147  cden = cden1
148  ELSE IF( abs( cnum1 ).GT.abs( cden ) ) THEN
149 *
150 * Pre-multiply X by BIGNUM if CDEN is small compared to CNUM.
151 *
152  mul = bignum
153  done = .false.
154  cnum = cnum1
155  ELSE
156 *
157 * Multiply X by CNUM / CDEN and return.
158 *
159  mul = cnum / cden
160  done = .true.
161  END IF
162 *
163 * Scale the vector X by MUL
164 *
165  CALL zdscal( n, mul, sx, incx )
166 *
167  IF( .NOT.done )
168  \$ GO TO 10
169 *
170  RETURN
171 *
172 * End of ZDRSCL
173 *
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:65