amos/zuchk.f

   1       SUBROUTINE ZUCHK(YR, YI, NZ, ASCLE, TOL)
   2 C***BEGIN PROLOGUE  ZUCHK
   3 C***REFER TO ZSERI,ZUOIK,ZUNK1,ZUNK2,ZUNI1,ZUNI2,ZKSCL
   4 C
   5 C      Y ENTERS AS A SCALED QUANTITY WHOSE MAGNITUDE IS GREATER THAN
   6 C      EXP(-ALIM)=ASCLE=1.0E+3*D1MACH(1)/TOL. THE TEST IS MADE TO SEE
   7 C      IF THE MAGNITUDE OF THE REAL OR IMAGINARY PART WOULD UNDERFLOW
   8 C      WHEN Y IS SCALED (BY TOL) TO ITS PROPER VALUE. Y IS ACCEPTED
   9 C      IF THE UNDERFLOW IS AT LEAST ONE PRECISION BELOW THE MAGNITUDE
  10 C      OF THE LARGEST COMPONENT; OTHERWISE THE PHASE ANGLE DOES NOT HAVE
  11 C      ABSOLUTE ACCURACY AND AN UNDERFLOW IS ASSUMED.
  12 C
  13 C***ROUTINES CALLED  (NONE)
  14 C***END PROLOGUE  ZUCHK
  15 C
  16 C     COMPLEX Y
  17       DOUBLE PRECISION ASCLE, SS, ST, TOL, WR, WI, YR, YI
  18       INTEGER NZ
  19       NZ = 0
  20       WR = DABS(YR)
  21       WI = DABS(YI)
  22       ST = DMIN1(WR,WI)
  23       IF (ST.GT.ASCLE) RETURN
  24       SS = DMAX1(WR,WI)
  25       ST = ST/TOL
  26       IF (SS.LT.ST) NZ = 1
  27       RETURN
  28       END