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SUBROUTINE ZBIRY(ZR, ZI, ID, KODE, BIR, BII, IERR)
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C***BEGIN PROLOGUE ZBIRY
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C***DATE WRITTEN 830501 (YYMMDD)
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C***REVISION DATE 890801 (YYMMDD)
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C***KEYWORDS AIRY FUNCTION,BESSEL FUNCTIONS OF ORDER ONE THIRD
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C***AUTHOR AMOS, DONALD E., SANDIA NATIONAL LABORATORIES
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C***PURPOSE TO COMPUTE AIRY FUNCTIONS BI(Z) AND DBI(Z) FOR COMPLEX Z
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C ***A DOUBLE PRECISION ROUTINE***
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C ON KODE=1, CBIRY COMPUTES THE COMPLEX AIRY FUNCTION BI(Z) OR
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C ITS DERIVATIVE DBI(Z)/DZ ON ID=0 OR ID=1 RESPECTIVELY. ON
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C KODE=2, A SCALING OPTION CEXP(-AXZTA)*BI(Z) OR CEXP(-AXZTA)*
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C DBI(Z)/DZ IS PROVIDED TO REMOVE THE EXPONENTIAL BEHAVIOR IN
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C BOTH THE LEFT AND RIGHT HALF PLANES WHERE
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C ZTA=(2/3)*Z*CSQRT(Z)=CMPLX(XZTA,YZTA) AND AXZTA=ABS(XZTA).
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C DEFINTIONS AND NOTATION ARE FOUND IN THE NBS HANDBOOK OF
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C MATHEMATICAL FUNCTIONS (REF. 1).
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C INPUT ZR,ZI ARE DOUBLE PRECISION
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C ZR,ZI - Z=CMPLX(ZR,ZI)
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C ID - ORDER OF DERIVATIVE, ID=0 OR ID=1
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C KODE - A PARAMETER TO INDICATE THE SCALING OPTION
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C BI=DBI(Z)/DZ ON ID=1
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C BI=CEXP(-AXZTA)*BI(Z) ON ID=0 OR
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C BI=CEXP(-AXZTA)*DBI(Z)/DZ ON ID=1 WHERE
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C ZTA=(2/3)*Z*CSQRT(Z)=CMPLX(XZTA,YZTA)
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C OUTPUT BIR,BII ARE DOUBLE PRECISION
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C BIR,BII- COMPLEX ANSWER DEPENDING ON THE CHOICES FOR ID AND
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C IERR=0, NORMAL RETURN - COMPUTATION COMPLETED
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C IERR=1, INPUT ERROR - NO COMPUTATION
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C IERR=2, OVERFLOW - NO COMPUTATION, REAL(Z)
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C IERR=3, CABS(Z) LARGE - COMPUTATION COMPLETED
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C LOSSES OF SIGNIFCANCE BY ARGUMENT REDUCTION
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C PRODUCE LESS THAN HALF OF MACHINE ACCURACY
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C IERR=4, CABS(Z) TOO LARGE - NO COMPUTATION
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C COMPLETE LOSS OF ACCURACY BY ARGUMENT
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C IERR=5, ERROR - NO COMPUTATION,
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C ALGORITHM TERMINATION CONDITION NOT MET
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C BI AND DBI ARE COMPUTED FOR CABS(Z).GT.1.0 FROM THE I BESSEL
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C BI(Z)=C*SQRT(Z)*( I(-1/3,ZTA) + I(1/3,ZTA) )
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C DBI(Z)=C * Z * ( I(-2/3,ZTA) + I(2/3,ZTA) )
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C WITH THE POWER SERIES FOR CABS(Z).LE.1.0.
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C IN MOST COMPLEX VARIABLE COMPUTATION, ONE MUST EVALUATE ELE-
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C MENTARY FUNCTIONS. WHEN THE MAGNITUDE OF Z IS LARGE, LOSSES
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C OF SIGNIFICANCE BY ARGUMENT REDUCTION OCCUR. CONSEQUENTLY, IF
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C THE MAGNITUDE OF ZETA=(2/3)*Z**1.5 EXCEEDS U1=SQRT(0.5/UR),
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C THEN LOSSES EXCEEDING HALF PRECISION ARE LIKELY AND AN ERROR
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C FLAG IERR=3 IS TRIGGERED WHERE UR=DMAX1(D1MACH(4),1.0D-18) IS
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C DOUBLE PRECISION UNIT ROUNDOFF LIMITED TO 18 DIGITS PRECISION.
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C ALSO, IF THE MAGNITUDE OF ZETA IS LARGER THAN U2=0.5/UR, THEN
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C ALL SIGNIFICANCE IS LOST AND IERR=4. IN ORDER TO USE THE INT
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C FUNCTION, ZETA MUST BE FURTHER RESTRICTED NOT TO EXCEED THE
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C LARGEST INTEGER, U3=I1MACH(9). THUS, THE MAGNITUDE OF ZETA
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C MUST BE RESTRICTED BY MIN(U2,U3). ON 32 BIT MACHINES, U1,U2,
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C AND U3 ARE APPROXIMATELY 2.0E+3, 4.2E+6, 2.1E+9 IN SINGLE
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C PRECISION ARITHMETIC AND 1.3E+8, 1.8E+16, 2.1E+9 IN DOUBLE
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C PRECISION ARITHMETIC RESPECTIVELY. THIS MAKES U2 AND U3 LIMIT-
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C ING IN THEIR RESPECTIVE ARITHMETICS. THIS MEANS THAT THE MAG-
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C NITUDE OF Z CANNOT EXCEED 3.1E+4 IN SINGLE AND 2.1E+6 IN
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C DOUBLE PRECISION ARITHMETIC. THIS ALSO MEANS THAT ONE CAN
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C EXPECT TO RETAIN, IN THE WORST CASES ON 32 BIT MACHINES,
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C NO DIGITS IN SINGLE PRECISION AND ONLY 7 DIGITS IN DOUBLE
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C PRECISION ARITHMETIC. SIMILAR CONSIDERATIONS HOLD FOR OTHER
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C THE APPROXIMATE RELATIVE ERROR IN THE MAGNITUDE OF A COMPLEX
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C BESSEL FUNCTION CAN BE EXPRESSED BY P*10**S WHERE P=MAX(UNIT
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C ROUNDOFF,1.0E-18) IS THE NOMINAL PRECISION AND 10**S REPRE-
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C SENTS THE INCREASE IN ERROR DUE TO ARGUMENT REDUCTION IN THE
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C ELEMENTARY FUNCTIONS. HERE, S=MAX(1,ABS(LOG10(CABS(Z))),
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C ABS(LOG10(FNU))) APPROXIMATELY (I.E. S=MAX(1,ABS(EXPONENT OF
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C CABS(Z),ABS(EXPONENT OF FNU)) ). HOWEVER, THE PHASE ANGLE MAY
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C HAVE ONLY ABSOLUTE ACCURACY. THIS IS MOST LIKELY TO OCCUR WHEN
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C ONE COMPONENT (IN ABSOLUTE VALUE) IS LARGER THAN THE OTHER BY
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C SEVERAL ORDERS OF MAGNITUDE. IF ONE COMPONENT IS 10**K LARGER
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C THAN THE OTHER, THEN ONE CAN EXPECT ONLY MAX(ABS(LOG10(P))-K,
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C 0) SIGNIFICANT DIGITS; OR, STATED ANOTHER WAY, WHEN K EXCEEDS
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C THE EXPONENT OF P, NO SIGNIFICANT DIGITS REMAIN IN THE SMALLER
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C COMPONENT. HOWEVER, THE PHASE ANGLE RETAINS ABSOLUTE ACCURACY
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C BECAUSE, IN COMPLEX ARITHMETIC WITH PRECISION P, THE SMALLER
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C COMPONENT WILL NOT (AS A RULE) DECREASE BELOW P TIMES THE
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C MAGNITUDE OF THE LARGER COMPONENT. IN THESE EXTREME CASES,
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C THE PRINCIPAL PHASE ANGLE IS ON THE ORDER OF +P, -P, PI/2-P,
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C***REFERENCES HANDBOOK OF MATHEMATICAL FUNCTIONS BY M. ABRAMOWITZ
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C AND I. A. STEGUN, NBS AMS SERIES 55, U.S. DEPT. OF
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C COMPUTATION OF BESSEL FUNCTIONS OF COMPLEX ARGUMENT
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C AND LARGE ORDER BY D. E. AMOS, SAND83-0643, MAY, 1983
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C A SUBROUTINE PACKAGE FOR BESSEL FUNCTIONS OF A COMPLEX
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C ARGUMENT AND NONNEGATIVE ORDER BY D. E. AMOS, SAND85-
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C A PORTABLE PACKAGE FOR BESSEL FUNCTIONS OF A COMPLEX
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C ARGUMENT AND NONNEGATIVE ORDER BY D. E. AMOS, TRANS.
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C MATH. SOFTWARE, 1986
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C***ROUTINES CALLED ZBINU,XZABS,ZDIV,XZSQRT,D1MACH,I1MACH
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C***END PROLOGUE ZBIRY
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C COMPLEX BI,CONE,CSQ,CY,S1,S2,TRM1,TRM2,Z,ZTA,Z3
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DOUBLE PRECISION AA, AD, AK, ALIM, ATRM, AZ, AZ3, BB, BII, BIR,
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* BK, CC, CK, COEF, CONEI, CONER, CSQI, CSQR, CYI, CYR, C1, C2,
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* DIG, DK, D1, D2, EAA, ELIM, FID, FMR, FNU, FNUL, PI, RL, R1M5,
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* SFAC, STI, STR, S1I, S1R, S2I, S2R, TOL, TRM1I, TRM1R, TRM2I,
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* TRM2R, TTH, ZI, ZR, ZTAI, ZTAR, Z3I, Z3R, D1MACH, XZABS
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INTEGER ID, IERR, K, KODE, K1, K2, NZ, I1MACH
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DIMENSION CYR(2), CYI(2)
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DATA TTH, C1, C2, COEF, PI /6.66666666666666667D-01,
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* 6.14926627446000736D-01,4.48288357353826359D-01,
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* 5.77350269189625765D-01,3.14159265358979324D+00/
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DATA CONER, CONEI /1.0D0,0.0D0/
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C***FIRST EXECUTABLE STATEMENT ZBIRY
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IF (ID.LT.0 .OR. ID.GT.1) IERR=1
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IF (KODE.LT.1 .OR. KODE.GT.2) IERR=1
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IF (IERR.NE.0) RETURN
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TOL = DMAX1(D1MACH(4),1.0D-18)
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FID = DBLE(FLOAT(ID))
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IF (AZ.GT.1.0E0) GO TO 70
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C-----------------------------------------------------------------------
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C POWER SERIES FOR CABS(Z).LE.1.
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C-----------------------------------------------------------------------
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IF (AZ.LT.TOL) GO TO 130
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IF (AA.LT.TOL/AZ) GO TO 40
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Z3R = STR*ZR - STI*ZI
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Z3I = STR*ZI + STI*ZR
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BK = 3.0D0 - FID - FID
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DK = 3.0D0 + FID + FID
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AK = 24.0D0 + 9.0D0*FID
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BK = 30.0D0 - 9.0D0*FID
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STR = (TRM1R*Z3R-TRM1I*Z3I)/D1
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TRM1I = (TRM1R*Z3I+TRM1I*Z3R)/D1
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STR = (TRM2R*Z3R-TRM2I*Z3I)/D2
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TRM2I = (TRM2R*Z3I+TRM2I*Z3R)/D2
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IF (ATRM.LT.TOL*AD) GO TO 40
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IF (ID.EQ.1) GO TO 50
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BIR = C1*S1R + C2*(ZR*S2R-ZI*S2I)
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BII = C1*S1I + C2*(ZR*S2I+ZI*S2R)
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IF (KODE.EQ.1) RETURN
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CALL XZSQRT(ZR, ZI, STR, STI)
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ZTAR = TTH*(ZR*STR-ZI*STI)
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ZTAI = TTH*(ZR*STI+ZI*STR)
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IF (AZ.LE.TOL) GO TO 60
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STR = S1R*ZR - S1I*ZI
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STI = S1R*ZI + S1I*ZR
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BIR = BIR + CC*(STR*ZR-STI*ZI)
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BII = BII + CC*(STR*ZI+STI*ZR)
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IF (KODE.EQ.1) RETURN
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CALL XZSQRT(ZR, ZI, STR, STI)
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ZTAR = TTH*(ZR*STR-ZI*STI)
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ZTAI = TTH*(ZR*STI+ZI*STR)
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C-----------------------------------------------------------------------
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C CASE FOR CABS(Z).GT.1.0
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C-----------------------------------------------------------------------
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FNU = (1.0D0+FID)/3.0D0
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C-----------------------------------------------------------------------
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C SET PARAMETERS RELATED TO MACHINE CONSTANTS.
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C TOL IS THE APPROXIMATE UNIT ROUNDOFF LIMITED TO 1.0E-18.
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C ELIM IS THE APPROXIMATE EXPONENTIAL OVER- AND UNDERFLOW LIMIT.
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C EXP(-ELIM).LT.EXP(-ALIM)=EXP(-ELIM)/TOL AND
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C EXP(ELIM).GT.EXP(ALIM)=EXP(ELIM)*TOL ARE INTERVALS NEAR
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C UNDERFLOW AND OVERFLOW LIMITS WHERE SCALED ARITHMETIC IS DONE.
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C RL IS THE LOWER BOUNDARY OF THE ASYMPTOTIC EXPANSION FOR LARGE Z.
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C DIG = NUMBER OF BASE 10 DIGITS IN TOL = 10**(-DIG).
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C FNUL IS THE LOWER BOUNDARY OF THE ASYMPTOTIC SERIES FOR LARGE FNU.
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C-----------------------------------------------------------------------
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K = MIN0(IABS(K1),IABS(K2))
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ELIM = 2.303D0*(DBLE(FLOAT(K))*R1M5-3.0D0)
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AA = R1M5*DBLE(FLOAT(K1))
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DIG = DMIN1(AA,18.0D0)
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ALIM = ELIM + DMAX1(-AA,-41.45D0)
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RL = 1.2D0*DIG + 3.0D0
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FNUL = 10.0D0 + 6.0D0*(DIG-3.0D0)
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C-----------------------------------------------------------------------
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C-----------------------------------------------------------------------
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BB=DBLE(FLOAT(I1MACH(9)))*0.5D0
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IF (AZ.GT.AA) GO TO 260
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CALL XZSQRT(ZR, ZI, CSQR, CSQI)
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ZTAR = TTH*(ZR*CSQR-ZI*CSQI)
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ZTAI = TTH*(ZR*CSQI+ZI*CSQR)
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C-----------------------------------------------------------------------
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C RE(ZTA).LE.0 WHEN RE(Z).LT.0, ESPECIALLY WHEN IM(Z) IS SMALL
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C-----------------------------------------------------------------------
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IF (ZR.GE.0.0D0) GO TO 80
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IF (ZI.NE.0.0D0 .OR. ZR.GT.0.0D0) GO TO 90
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IF (KODE.EQ.2) GO TO 100
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C-----------------------------------------------------------------------
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C-----------------------------------------------------------------------
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IF (BB.LT.ALIM) GO TO 100
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BB = BB + 0.25D0*DLOG(AZ)
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IF (BB.GT.ELIM) GO TO 190
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IF (AA.GE.0.0D0 .AND. ZR.GT.0.0D0) GO TO 110
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IF (ZI.LT.0.0D0) FMR = -PI
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C-----------------------------------------------------------------------
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C AA=FACTOR FOR ANALYTIC CONTINUATION OF I(FNU,ZTA)
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C KODE=2 RETURNS EXP(-ABS(XZTA))*I(FNU,ZTA) FROM CBESI
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C-----------------------------------------------------------------------
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CALL ZBINU(ZTAR, ZTAI, FNU, KODE, 1, CYR, CYI, NZ, RL, FNUL, TOL,
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IF (NZ.LT.0) GO TO 200
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S1R = (STR*CYR(1)-STI*CYI(1))*Z3R
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S1I = (STR*CYI(1)+STI*CYR(1))*Z3R
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FNU = (2.0D0-FID)/3.0D0
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CALL ZBINU(ZTAR, ZTAI, FNU, KODE, 2, CYR, CYI, NZ, RL, FNUL, TOL,
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C-----------------------------------------------------------------------
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C BACKWARD RECUR ONE STEP FOR ORDERS -1/3 OR -2/3
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C-----------------------------------------------------------------------
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CALL ZDIV(CYR(1), CYI(1), ZTAR, ZTAI, STR, STI)
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S2R = (FNU+FNU)*STR + CYR(2)
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S2I = (FNU+FNU)*STI + CYI(2)
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S1R = COEF*(S1R+S2R*STR-S2I*STI)
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S1I = COEF*(S1I+S2R*STI+S2I*STR)
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IF (ID.EQ.1) GO TO 120
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STR = CSQR*S1R - CSQI*S1I
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S1I = CSQR*S1I + CSQI*S1R
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STR = ZR*S1R - ZI*S1I
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S1I = ZR*S1I + ZI*S1R
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AA = C1*(1.0D0-FID) + FID*C2
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IF(NZ.EQ.(-1)) GO TO 190
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libcruft/amos/zbiry.f
