zuchk.f

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00001       SUBROUTINE ZUCHK(YR, YI, NZ, ASCLE, TOL)
00002 C***BEGIN PROLOGUE  ZUCHK
00003 C***REFER TO ZSERI,ZUOIK,ZUNK1,ZUNK2,ZUNI1,ZUNI2,ZKSCL
00004 C
00005 C      Y ENTERS AS A SCALED QUANTITY WHOSE MAGNITUDE IS GREATER THAN
00006 C      EXP(-ALIM)=ASCLE=1.0E+3*D1MACH(1)/TOL. THE TEST IS MADE TO SEE
00007 C      IF THE MAGNITUDE OF THE REAL OR IMAGINARY PART WOULD UNDERFLOW
00008 C      WHEN Y IS SCALED (BY TOL) TO ITS PROPER VALUE. Y IS ACCEPTED
00009 C      IF THE UNDERFLOW IS AT LEAST ONE PRECISION BELOW THE MAGNITUDE
00010 C      OF THE LARGEST COMPONENT; OTHERWISE THE PHASE ANGLE DOES NOT HAVE
00011 C      ABSOLUTE ACCURACY AND AN UNDERFLOW IS ASSUMED.
00012 C
00013 C***ROUTINES CALLED  (NONE)
00014 C***END PROLOGUE  ZUCHK
00015 C
00016 C     COMPLEX Y
00017       DOUBLE PRECISION ASCLE, SS, ST, TOL, WR, WI, YR, YI
00018       INTEGER NZ
00019       NZ = 0
00020       WR = DABS(YR)
00021       WI = DABS(YI)
00022       ST = DMIN1(WR,WI)
00023       IF (ST.GT.ASCLE) RETURN
00024       SS = DMAX1(WR,WI)
00025       ST = ST/TOL
00026       IF (SS.LT.ST) NZ = 1
00027       RETURN
00028       END
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