SUBROUTINE ZAIRY(ZR, ZI, ID, KODE, AIR, AII, NZ, IERR) C***BEGIN PROLOGUE ZAIRY C***DATE WRITTEN 830501 (YYMMDD) C***REVISION DATE 890801 (YYMMDD) C***CATEGORY NO. B5K C***KEYWORDS AIRY FUNCTION,BESSEL FUNCTIONS OF ORDER ONE THIRD C***AUTHOR AMOS, DONALD E., SANDIA NATIONAL LABORATORIES C***PURPOSE TO COMPUTE AIRY FUNCTIONS AI(Z) AND DAI(Z) FOR COMPLEX Z C***DESCRIPTION C C ***A DOUBLE PRECISION ROUTINE*** C ON KODE=1, ZAIRY COMPUTES THE COMPLEX AIRY FUNCTION AI(Z) OR C ITS DERIVATIVE DAI(Z)/DZ ON ID=0 OR ID=1 RESPECTIVELY. ON C KODE=2, A SCALING OPTION CEXP(ZTA)*AI(Z) OR CEXP(ZTA)* C DAI(Z)/DZ IS PROVIDED TO REMOVE THE EXPONENTIAL DECAY IN C -PI/3.LT.ARG(Z).LT.PI/3 AND THE EXPONENTIAL GROWTH IN C PI/3.LT.ABS(ARG(Z)).LT.PI WHERE ZTA=(2/3)*Z*CSQRT(Z). C C WHILE THE AIRY FUNCTIONS AI(Z) AND DAI(Z)/DZ ARE ANALYTIC IN C THE WHOLE Z PLANE, THE CORRESPONDING SCALED FUNCTIONS DEFINED C FOR KODE=2 HAVE A CUT ALONG THE NEGATIVE REAL AXIS. C DEFINITIONS AND NOTATION ARE FOUND IN THE NBS HANDBOOK OF C MATHEMATICAL FUNCTIONS (REF. 1). C C INPUT ZR,ZI ARE DOUBLE PRECISION C ZR,ZI - Z=CMPLX(ZR,ZI) C ID - ORDER OF DERIVATIVE, ID=0 OR ID=1 C KODE - A PARAMETER TO INDICATE THE SCALING OPTION C KODE= 1 RETURNS C AI=AI(Z) ON ID=0 OR C AI=DAI(Z)/DZ ON ID=1 C = 2 RETURNS C AI=CEXP(ZTA)*AI(Z) ON ID=0 OR C AI=CEXP(ZTA)*DAI(Z)/DZ ON ID=1 WHERE C ZTA=(2/3)*Z*CSQRT(Z) C C OUTPUT AIR,AII ARE DOUBLE PRECISION C AIR,AII- COMPLEX ANSWER DEPENDING ON THE CHOICES FOR ID AND C KODE C NZ - UNDERFLOW INDICATOR C NZ= 0 , NORMAL RETURN C NZ= 1 , AI=CMPLX(0.0D0,0.0D0) DUE TO UNDERFLOW IN C -PI/3.LT.ARG(Z).LT.PI/3 ON KODE=1 C IERR - ERROR FLAG C IERR=0, NORMAL RETURN - COMPUTATION COMPLETED C IERR=1, INPUT ERROR - NO COMPUTATION C IERR=2, OVERFLOW - NO COMPUTATION, REAL(ZTA) C TOO LARGE ON KODE=1 C IERR=3, CABS(Z) LARGE - COMPUTATION COMPLETED C LOSSES OF SIGNIFCANCE BY ARGUMENT REDUCTION C PRODUCE LESS THAN HALF OF MACHINE ACCURACY C IERR=4, CABS(Z) TOO LARGE - NO COMPUTATION C COMPLETE LOSS OF ACCURACY BY ARGUMENT C REDUCTION C IERR=5, ERROR - NO COMPUTATION, C ALGORITHM TERMINATION CONDITION NOT MET C C***LONG DESCRIPTION C C AI AND DAI ARE COMPUTED FOR CABS(Z).GT.1.0 FROM THE K BESSEL C FUNCTIONS BY C C AI(Z)=C*SQRT(Z)*K(1/3,ZTA) , DAI(Z)=-C*Z*K(2/3,ZTA) C C=1.0/(PI*SQRT(3.0)) C ZTA=(2/3)*Z**(3/2) C C WITH THE POWER SERIES FOR CABS(Z).LE.1.0. C C IN MOST COMPLEX VARIABLE COMPUTATION, ONE MUST EVALUATE ELE- C MENTARY FUNCTIONS. WHEN THE MAGNITUDE OF Z IS LARGE, LOSSES C OF SIGNIFICANCE BY ARGUMENT REDUCTION OCCUR. CONSEQUENTLY, IF C THE MAGNITUDE OF ZETA=(2/3)*Z**1.5 EXCEEDS U1=SQRT(0.5/UR), C THEN LOSSES EXCEEDING HALF PRECISION ARE LIKELY AND AN ERROR C FLAG IERR=3 IS TRIGGERED WHERE UR=DMAX1(D1MACH(4),1.0D-18) IS C DOUBLE PRECISION UNIT ROUNDOFF LIMITED TO 18 DIGITS PRECISION. C ALSO, IF THE MAGNITUDE OF ZETA IS LARGER THAN U2=0.5/UR, THEN C ALL SIGNIFICANCE IS LOST AND IERR=4. IN ORDER TO USE THE INT C FUNCTION, ZETA MUST BE FURTHER RESTRICTED NOT TO EXCEED THE C LARGEST INTEGER, U3=I1MACH(9). THUS, THE MAGNITUDE OF ZETA C MUST BE RESTRICTED BY MIN(U2,U3). ON 32 BIT MACHINES, U1,U2, C AND U3 ARE APPROXIMATELY 2.0E+3, 4.2E+6, 2.1E+9 IN SINGLE C PRECISION ARITHMETIC AND 1.3E+8, 1.8E+16, 2.1E+9 IN DOUBLE C PRECISION ARITHMETIC RESPECTIVELY. THIS MAKES U2 AND U3 LIMIT- C ING IN THEIR RESPECTIVE ARITHMETICS. THIS MEANS THAT THE MAG- C NITUDE OF Z CANNOT EXCEED 3.1E+4 IN SINGLE AND 2.1E+6 IN C DOUBLE PRECISION ARITHMETIC. THIS ALSO MEANS THAT ONE CAN C EXPECT TO RETAIN, IN THE WORST CASES ON 32 BIT MACHINES, C NO DIGITS IN SINGLE PRECISION AND ONLY 7 DIGITS IN DOUBLE C PRECISION ARITHMETIC. SIMILAR CONSIDERATIONS HOLD FOR OTHER C MACHINES. C C THE APPROXIMATE RELATIVE ERROR IN THE MAGNITUDE OF A COMPLEX C BESSEL FUNCTION CAN BE EXPRESSED BY P*10**S WHERE P=MAX(UNIT C ROUNDOFF,1.0E-18) IS THE NOMINAL PRECISION AND 10**S REPRE- C SENTS THE INCREASE IN ERROR DUE TO ARGUMENT REDUCTION IN THE C ELEMENTARY FUNCTIONS. HERE, S=MAX(1,ABS(LOG10(CABS(Z))), C ABS(LOG10(FNU))) APPROXIMATELY (I.E. S=MAX(1,ABS(EXPONENT OF C CABS(Z),ABS(EXPONENT OF FNU)) ). HOWEVER, THE PHASE ANGLE MAY C HAVE ONLY ABSOLUTE ACCURACY. THIS IS MOST LIKELY TO OCCUR WHEN C ONE COMPONENT (IN ABSOLUTE VALUE) IS LARGER THAN THE OTHER BY C SEVERAL ORDERS OF MAGNITUDE. IF ONE COMPONENT IS 10**K LARGER C THAN THE OTHER, THEN ONE CAN EXPECT ONLY MAX(ABS(LOG10(P))-K, C 0) SIGNIFICANT DIGITS; OR, STATED ANOTHER WAY, WHEN K EXCEEDS C THE EXPONENT OF P, NO SIGNIFICANT DIGITS REMAIN IN THE SMALLER C COMPONENT. HOWEVER, THE PHASE ANGLE RETAINS ABSOLUTE ACCURACY C BECAUSE, IN COMPLEX ARITHMETIC WITH PRECISION P, THE SMALLER C COMPONENT WILL NOT (AS A RULE) DECREASE BELOW P TIMES THE C MAGNITUDE OF THE LARGER COMPONENT. IN THESE EXTREME CASES, C THE PRINCIPAL PHASE ANGLE IS ON THE ORDER OF +P, -P, PI/2-P, C OR -PI/2+P. C C***REFERENCES HANDBOOK OF MATHEMATICAL FUNCTIONS BY M. ABRAMOWITZ C AND I. A. STEGUN, NBS AMS SERIES 55, U.S. DEPT. OF C COMMERCE, 1955. C C COMPUTATION OF BESSEL FUNCTIONS OF COMPLEX ARGUMENT C AND LARGE ORDER BY D. E. AMOS, SAND83-0643, MAY, 1983 C C A SUBROUTINE PACKAGE FOR BESSEL FUNCTIONS OF A COMPLEX C ARGUMENT AND NONNEGATIVE ORDER BY D. E. AMOS, SAND85- C 1018, MAY, 1985 C C A PORTABLE PACKAGE FOR BESSEL FUNCTIONS OF A COMPLEX C ARGUMENT AND NONNEGATIVE ORDER BY D. E. AMOS, TRANS. C MATH. SOFTWARE, 1986 C C***ROUTINES CALLED ZACAI,ZBKNU,AZEXP,AZSQRT,I1MACH,D1MACH C***END PROLOGUE ZAIRY C COMPLEX AI,CONE,CSQ,CY,S1,S2,TRM1,TRM2,Z,ZTA,Z3 DOUBLE PRECISION AA, AD, AII, AIR, AK, ALIM, ATRM, AZ, AZ3, BK, * CC, CK, COEF, CONEI, CONER, CSQI, CSQR, CYI, CYR, C1, C2, DIG, * DK, D1, D2, ELIM, FID, FNU, PTR, RL, R1M5, SFAC, STI, STR, * S1I, S1R, S2I, S2R, TOL, TRM1I, TRM1R, TRM2I, TRM2R, TTH, ZEROI, * ZEROR, ZI, ZR, ZTAI, ZTAR, Z3I, Z3R, D1MACH, AZABS, ALAZ, BB INTEGER ID, IERR, IFLAG, K, KODE, K1, K2, MR, NN, NZ, I1MACH DIMENSION CYR(1), CYI(1) DATA TTH, C1, C2, COEF /6.66666666666666667D-01, * 3.55028053887817240D-01,2.58819403792806799D-01, * 1.83776298473930683D-01/ DATA ZEROR, ZEROI, CONER, CONEI /0.0D0,0.0D0,1.0D0,0.0D0/ C***FIRST EXECUTABLE STATEMENT ZAIRY IERR = 0 NZ=0 IF (ID.LT.0 .OR. ID.GT.1) IERR=1 IF (KODE.LT.1 .OR. KODE.GT.2) IERR=1 IF (IERR.NE.0) RETURN AZ = AZABS(ZR,ZI) TOL = DMAX1(D1MACH(4),1.0D-18) FID = DBLE(FLOAT(ID)) IF (AZ.GT.1.0D0) GO TO 70 C----------------------------------------------------------------------- C POWER SERIES FOR CABS(Z).LE.1. C----------------------------------------------------------------------- S1R = CONER S1I = CONEI S2R = CONER S2I = CONEI IF (AZ.LT.TOL) GO TO 170 AA = AZ*AZ IF (AA.LT.TOL/AZ) GO TO 40 TRM1R = CONER TRM1I = CONEI TRM2R = CONER TRM2I = CONEI ATRM = 1.0D0 STR = ZR*ZR - ZI*ZI STI = ZR*ZI + ZI*ZR Z3R = STR*ZR - STI*ZI Z3I = STR*ZI + STI*ZR AZ3 = AZ*AA AK = 2.0D0 + FID BK = 3.0D0 - FID - FID CK = 4.0D0 - FID DK = 3.0D0 + FID + FID D1 = AK*DK D2 = BK*CK AD = DMIN1(D1,D2) AK = 24.0D0 + 9.0D0*FID BK = 30.0D0 - 9.0D0*FID DO 30 K=1,25 STR = (TRM1R*Z3R-TRM1I*Z3I)/D1 TRM1I = (TRM1R*Z3I+TRM1I*Z3R)/D1 TRM1R = STR S1R = S1R + TRM1R S1I = S1I + TRM1I STR = (TRM2R*Z3R-TRM2I*Z3I)/D2 TRM2I = (TRM2R*Z3I+TRM2I*Z3R)/D2 TRM2R = STR S2R = S2R + TRM2R S2I = S2I + TRM2I ATRM = ATRM*AZ3/AD D1 = D1 + AK D2 = D2 + BK AD = DMIN1(D1,D2) IF (ATRM.LT.TOL*AD) GO TO 40 AK = AK + 18.0D0 BK = BK + 18.0D0 30 CONTINUE 40 CONTINUE IF (ID.EQ.1) GO TO 50 AIR = S1R*C1 - C2*(ZR*S2R-ZI*S2I) AII = S1I*C1 - C2*(ZR*S2I+ZI*S2R) IF (KODE.EQ.1) RETURN CALL AZSQRT(ZR, ZI, STR, STI) ZTAR = TTH*(ZR*STR-ZI*STI) ZTAI = TTH*(ZR*STI+ZI*STR) CALL AZEXP(ZTAR, ZTAI, STR, STI) PTR = AIR*STR - AII*STI AII = AIR*STI + AII*STR AIR = PTR RETURN 50 CONTINUE AIR = -S2R*C2 AII = -S2I*C2 IF (AZ.LE.TOL) GO TO 60 STR = ZR*S1R - ZI*S1I STI = ZR*S1I + ZI*S1R CC = C1/(1.0D0+FID) AIR = AIR + CC*(STR*ZR-STI*ZI) AII = AII + CC*(STR*ZI+STI*ZR) 60 CONTINUE IF (KODE.EQ.1) RETURN CALL AZSQRT(ZR, ZI, STR, STI) ZTAR = TTH*(ZR*STR-ZI*STI) ZTAI = TTH*(ZR*STI+ZI*STR) CALL AZEXP(ZTAR, ZTAI, STR, STI) PTR = STR*AIR - STI*AII AII = STR*AII + STI*AIR AIR = PTR RETURN C----------------------------------------------------------------------- C CASE FOR CABS(Z).GT.1.0 C----------------------------------------------------------------------- 70 CONTINUE FNU = (1.0D0+FID)/3.0D0 C----------------------------------------------------------------------- C SET PARAMETERS RELATED TO MACHINE CONSTANTS. C TOL IS THE APPROXIMATE UNIT ROUNDOFF LIMITED TO 1.0D-18. C ELIM IS THE APPROXIMATE EXPONENTIAL OVER- AND UNDERFLOW LIMIT. C EXP(-ELIM).LT.EXP(-ALIM)=EXP(-ELIM)/TOL AND C EXP(ELIM).GT.EXP(ALIM)=EXP(ELIM)*TOL ARE INTERVALS NEAR C UNDERFLOW AND OVERFLOW LIMITS WHERE SCALED ARITHMETIC IS DONE. C RL IS THE LOWER BOUNDARY OF THE ASYMPTOTIC EXPANSION FOR LARGE Z. C DIG = NUMBER OF BASE 10 DIGITS IN TOL = 10**(-DIG). C----------------------------------------------------------------------- K1 = I1MACH(15) K2 = I1MACH(16) R1M5 = D1MACH(5) K = MIN0(IABS(K1),IABS(K2)) ELIM = 2.303D0*(DBLE(FLOAT(K))*R1M5-3.0D0) K1 = I1MACH(14) - 1 AA = R1M5*DBLE(FLOAT(K1)) DIG = DMIN1(AA,18.0D0) AA = AA*2.303D0 ALIM = ELIM + DMAX1(-AA,-41.45D0) RL = 1.2D0*DIG + 3.0D0 ALAZ = DLOG(AZ) C-------------------------------------------------------------------------- C TEST FOR PROPER RANGE C----------------------------------------------------------------------- AA=0.5D0/TOL BB=DBLE(FLOAT(I1MACH(9)))*0.5D0 AA=DMIN1(AA,BB) AA=AA**TTH IF (AZ.GT.AA) GO TO 260 AA=DSQRT(AA) IF (AZ.GT.AA) IERR=3 CALL AZSQRT(ZR, ZI, CSQR, CSQI) ZTAR = TTH*(ZR*CSQR-ZI*CSQI) ZTAI = TTH*(ZR*CSQI+ZI*CSQR) C----------------------------------------------------------------------- C RE(ZTA).LE.0 WHEN RE(Z).LT.0, ESPECIALLY WHEN IM(Z) IS SMALL C----------------------------------------------------------------------- IFLAG = 0 SFAC = 1.0D0 AK = ZTAI IF (ZR.GE.0.0D0) GO TO 80 BK = ZTAR CK = -DABS(BK) ZTAR = CK ZTAI = AK 80 CONTINUE IF (ZI.NE.0.0D0) GO TO 90 IF (ZR.GT.0.0D0) GO TO 90 ZTAR = 0.0D0 ZTAI = AK 90 CONTINUE AA = ZTAR IF (AA.GE.0.0D0 .AND. ZR.GT.0.0D0) GO TO 110 IF (KODE.EQ.2) GO TO 100 C----------------------------------------------------------------------- C OVERFLOW TEST C----------------------------------------------------------------------- IF (AA.GT.(-ALIM)) GO TO 100 AA = -AA + 0.25D0*ALAZ IFLAG = 1 SFAC = TOL IF (AA.GT.ELIM) GO TO 270 100 CONTINUE C----------------------------------------------------------------------- C CBKNU AND CACON RETURN EXP(ZTA)*K(FNU,ZTA) ON KODE=2 C----------------------------------------------------------------------- MR = 1 IF (ZI.LT.0.0D0) MR = -1 CALL ZACAI(ZTAR, ZTAI, FNU, KODE, MR, 1, CYR, CYI, NN, RL, TOL, * ELIM, ALIM) IF (NN.LT.0) GO TO 280 NZ = NZ + NN GO TO 130 110 CONTINUE IF (KODE.EQ.2) GO TO 120 C----------------------------------------------------------------------- C UNDERFLOW TEST C----------------------------------------------------------------------- IF (AA.LT.ALIM) GO TO 120 AA = -AA - 0.25D0*ALAZ IFLAG = 2 SFAC = 1.0D0/TOL IF (AA.LT.(-ELIM)) GO TO 210 120 CONTINUE CALL ZBKNU(ZTAR, ZTAI, FNU, KODE, 1, CYR, CYI, NZ, TOL, ELIM, * ALIM) 130 CONTINUE S1R = CYR(1)*COEF S1I = CYI(1)*COEF IF (IFLAG.NE.0) GO TO 150 IF (ID.EQ.1) GO TO 140 AIR = CSQR*S1R - CSQI*S1I AII = CSQR*S1I + CSQI*S1R RETURN 140 CONTINUE AIR = -(ZR*S1R-ZI*S1I) AII = -(ZR*S1I+ZI*S1R) RETURN 150 CONTINUE S1R = S1R*SFAC S1I = S1I*SFAC IF (ID.EQ.1) GO TO 160 STR = S1R*CSQR - S1I*CSQI S1I = S1R*CSQI + S1I*CSQR S1R = STR AIR = S1R/SFAC AII = S1I/SFAC RETURN 160 CONTINUE STR = -(S1R*ZR-S1I*ZI) S1I = -(S1R*ZI+S1I*ZR) S1R = STR AIR = S1R/SFAC AII = S1I/SFAC RETURN 170 CONTINUE AA = 1.0D+3*D1MACH(1) S1R = ZEROR S1I = ZEROI IF (ID.EQ.1) GO TO 190 IF (AZ.LE.AA) GO TO 180 S1R = C2*ZR S1I = C2*ZI 180 CONTINUE AIR = C1 - S1R AII = -S1I RETURN 190 CONTINUE AIR = -C2 AII = 0.0D0 AA = DSQRT(AA) IF (AZ.LE.AA) GO TO 200 S1R = 0.5D0*(ZR*ZR-ZI*ZI) S1I = ZR*ZI 200 CONTINUE AIR = AIR + C1*S1R AII = AII + C1*S1I RETURN 210 CONTINUE NZ = 1 AIR = ZEROR AII = ZEROI RETURN 270 CONTINUE NZ = 0 IERR=2 RETURN 280 CONTINUE IF(NN.EQ.(-1)) GO TO 270 NZ=0 IERR=5 RETURN 260 CONTINUE IERR=4 NZ=0 RETURN END