SUBROUTINE RJBESL(X, ALPHA, NB, B, NCALC) C--------------------------------------------------------------------- C This routine calculates Bessel functions J sub(N+ALPHA) (X) C for non-negative argument X, and non-negative order N+ALPHA. C C C Explanation of variables in the calling sequence. C C X - working precision non-negative real argument for which C J's are to be calculated. C ALPHA - working precision fractional part of order for which C J's or exponentially scaled J'r (J*exp(X)) are C to be calculated. 0 <= ALPHA < 1.0. C NB - integer number of functions to be calculated, NB > 0. C The first function calculated is of order ALPHA, and the C last is of order (NB - 1 + ALPHA). C B - working precision output vector of length NB. If RJBESL C terminates normally (NCALC=NB), the vector B contains the C functions J/ALPHA/(X) through J/NB-1+ALPHA/(X), or the C corresponding exponentially scaled functions. C NCALC - integer output variable indicating possible errors. C Before using the vector B, the user should check that C NCALC=NB, i.e., all orders have been calculated to C the desired accuracy. See Error Returns below. C C C******************************************************************* C******************************************************************* C C Explanation of machine-dependent constants C C it = Number of bits in the mantissa of a working precision C variable C NSIG = Decimal significance desired. Should be set to C INT(LOG10(2)*it+1). Setting NSIG lower will result C in decreased accuracy while setting NSIG higher will C increase CPU time without increasing accuracy. The C truncation error is limited to a relative error of C T=.5*10**(-NSIG). C ENTEN = 10.0 ** K, where K is the largest integer such that C ENTEN is machine-representable in working precision C ENSIG = 10.0 ** NSIG C RTNSIG = 10.0 ** (-K) for the smallest integer K such that C K .GE. NSIG/4 C ENMTEN = Smallest ABS(X) such that X/4 does not underflow C XLARGE = Upper limit on the magnitude of X. If ABS(X)=N, C then at least N iterations of the backward recursion C will be executed. The value of 10.0 ** 4 is used on C every machine. C C C Approximate values for some important machines are: C C C it NSIG ENTEN ENSIG C C CRAY-1 (S.P.) 48 15 1.0E+2465 1.0E+15 C Cyber 180/855 C under NOS (S.P.) 48 15 1.0E+322 1.0E+15 C IEEE (IBM/XT, C SUN, etc.) (S.P.) 24 8 1.0E+38 1.0E+8 C IEEE (IBM/XT, C SUN, etc.) (D.P.) 53 16 1.0D+308 1.0D+16 C IBM 3033 (D.P.) 14 5 1.0D+75 1.0D+5 C VAX (S.P.) 24 8 1.0E+38 1.0E+8 C VAX D-Format (D.P.) 56 17 1.0D+38 1.0D+17 C VAX G-Format (D.P.) 53 16 1.0D+307 1.0D+16 C C C RTNSIG ENMTEN XLARGE C C CRAY-1 (S.P.) 1.0E-4 1.84E-2466 1.0E+4 C Cyber 180/855 C under NOS (S.P.) 1.0E-4 1.25E-293 1.0E+4 C IEEE (IBM/XT, C SUN, etc.) (S.P.) 1.0E-2 4.70E-38 1.0E+4 C IEEE (IBM/XT, C SUN, etc.) (D.P.) 1.0E-4 8.90D-308 1.0D+4 C IBM 3033 (D.P.) 1.0E-2 2.16D-78 1.0D+4 C VAX (S.P.) 1.0E-2 1.17E-38 1.0E+4 C VAX D-Format (D.P.) 1.0E-5 1.17D-38 1.0D+4 C VAX G-Format (D.P.) 1.0E-4 2.22D-308 1.0D+4 C C******************************************************************* C******************************************************************* C C Error returns C C In case of an error, NCALC .NE. NB, and not all J's are C calculated to the desired accuracy. C C NCALC .LT. 0: An argument is out of range. For example, C NBES .LE. 0, ALPHA .LT. 0 or .GT. 1, or X is too large. C In this case, B(1) is set to zero, the remainder of the C B-vector is not calculated, and NCALC is set to C MIN(NB,0)-1 so that NCALC .NE. NB. C C NB .GT. NCALC .GT. 0: Not all requested function values could C be calculated accurately. This usually occurs because NB is C much larger than ABS(X). In this case, B(N) is calculated C to the desired accuracy for N .LE. NCALC, but precision C is lost for NCALC .LT. N .LE. NB. If B(N) does not vanish C for N .GT. NCALC (because it is too small to be represented), C and B(N)/B(NCALC) = 10**(-K), then only the first NSIG-K C significant figures of B(N) can be trusted. C C C Intrinsic and other functions required are: C C ABS, AINT, COS, DBLE, GAMMA (or DGAMMA), INT, MAX, MIN, C C REAL, SIN, SQRT C C C Acknowledgement C C This program is based on a program written by David J. Sookne C (2) that computes values of the Bessel functions J or I of real C argument and integer order. Modifications include the restriction C of the computation to the J Bessel function of non-negative real C argument, the extension of the computation to arbitrary positive C order, and the elimination of most underflow. C C References: "A Note on Backward Recurrence Algorithms," Olver, C F. W. J., and Sookne, D. J., Math. Comp. 26, 1972, C pp 941-947. C C "Bessel Functions of Real Argument and Integer Order," C Sookne, D. J., NBS Jour. of Res. B. 77B, 1973, pp C 125-132. C C Latest modification: March 19, 1990 C C Author: W. J. Cody C Applied Mathematics Division C Argonne National Laboratory C Argonne, IL 60439 C C--------------------------------------------------------------------- INTEGER I,J,K,L,M,MAGX,N,NB,NBMX,NCALC,NEND,NSTART CS REAL GAMMA, CD DOUBLE PRECISION DGAMMA, 1 ALPHA,ALPEM,ALP2EM,B,CAPP,CAPQ,CONV,EIGHTH,EM,EN,ENMTEN,ENSIG, 2 ENTEN,FACT,FOUR,FUNC,GNU,HALF,HALFX,ONE,ONE30,P,PI2,PLAST, 3 POLD,PSAVE,PSAVEL,RTNSIG,S,SUM,T,T1,TEMPA,TEMPB,TEMPC,TEST, 4 THREE,THREE5,TOVER,TWO,TWOFIV,TWOPI1,TWOPI2,X,XC,XIN,XK,XLARGE, 5 XM,VCOS,VSIN,Z,ZERO DIMENSION B(NB), FACT(25) C--------------------------------------------------------------------- C Mathematical constants C C PI2 - 2 / PI C TWOPI1 - first few significant digits of 2 * PI C TWOPI2 - (2*PI - TWOPI) to working precision, i.e., C TWOPI1 + TWOPI2 = 2 * PI to extra precision. C--------------------------------------------------------------------- CS DATA PI2, TWOPI1, TWOPI2 /0.636619772367581343075535E0,6.28125E0, CS 1 1.935307179586476925286767E-3/ CS DATA ZERO, EIGHTH, HALF, ONE /0.0E0,0.125E0,0.5E0,1.0E0/ CS DATA TWO, THREE, FOUR, TWOFIV /2.0E0,3.0E0,4.0E0,25.0E0/ CS DATA ONE30, THREE5 /130.0E0,35.0E0/ CD DATA PI2, TWOPI1, TWOPI2 /0.636619772367581343075535D0,6.28125D0, CD 1 1.935307179586476925286767D-3/ CD DATA ZERO, EIGHTH, HALF, ONE /0.0D0,0.125D0,0.5D0,1.0D0/ CD DATA TWO, THREE, FOUR, TWOFIV /2.0D0,3.0D0,4.0D0,25.0D0/ CD DATA ONE30, THREE5 /130.0D0,35.0D0/ C--------------------------------------------------------------------- C Machine-dependent parameters C--------------------------------------------------------------------- CS DATA ENTEN, ENSIG, RTNSIG /1.0E38,1.0E8,1.0E-2/ CS DATA ENMTEN, XLARGE /1.2E-37,1.0E4/ CD DATA ENTEN, ENSIG, RTNSIG /1.0D38,1.0D17,1.0D-4/ CD DATA ENMTEN, XLARGE /1.2D-37,1.0D4/ C--------------------------------------------------------------------- C Factorial(N) C--------------------------------------------------------------------- CS DATA FACT /1.0E0,1.0E0,2.0E0,6.0E0,24.0E0,1.2E2,7.2E2,5.04E3, CS 1 4.032E4,3.6288E5,3.6288E6,3.99168E7,4.790016E8,6.2270208E9, CS 2 8.71782912E10,1.307674368E12,2.0922789888E13,3.55687428096E14, CS 3 6.402373705728E15,1.21645100408832E17,2.43290200817664E18, CS 4 5.109094217170944E19,1.12400072777760768E21, CS 5 2.585201673888497664E22,6.2044840173323943936E23/ CD DATA FACT /1.0D0,1.0D0,2.0D0,6.0D0,24.0D0,1.2D2,7.2D2,5.04D3, CD 1 4.032D4,3.6288D5,3.6288D6,3.99168D7,4.790016D8,6.2270208D9, CD 2 8.71782912D10,1.307674368D12,2.0922789888D13,3.55687428096D14, CD 3 6.402373705728D15,1.21645100408832D17,2.43290200817664D18, CD 4 5.109094217170944D19,1.12400072777760768D21, CD 5 2.585201673888497664D22,6.2044840173323943936D23/ C--------------------------------------------------------------------- C Statement functions for conversion and the gamma function. C--------------------------------------------------------------------- CS CONV(I) = REAL(I) CS FUNC(X) = GAMMA(X) CD CONV(I) = DBLE(I) CD FUNC(X) = DGAMMA(X) C--------------------------------------------------------------------- C Check for out of range arguments. C--------------------------------------------------------------------- MAGX = INT(X) IF ((NB.GT.0) .AND. (X.GE.ZERO) .AND. (X.LE.XLARGE) 1 .AND. (ALPHA.GE.ZERO) .AND. (ALPHA.LT.ONE)) 2 THEN C--------------------------------------------------------------------- C Initialize result array to zero. C--------------------------------------------------------------------- NCALC = NB DO 20 I=1,NB B(I) = ZERO 20 CONTINUE C--------------------------------------------------------------------- C Branch to use 2-term ascending series for small X and asymptotic C form for large X when NB is not too large. C--------------------------------------------------------------------- IF (X.LT.RTNSIG) THEN C--------------------------------------------------------------------- C Two-term ascending series for small X. C--------------------------------------------------------------------- TEMPA = ONE ALPEM = ONE + ALPHA HALFX = ZERO IF (X.GT.ENMTEN) HALFX = HALF*X IF (ALPHA.NE.ZERO) 1 TEMPA = HALFX**ALPHA/(ALPHA*FUNC(ALPHA)) TEMPB = ZERO IF ((X+ONE).GT.ONE) TEMPB = -HALFX*HALFX B(1) = TEMPA + TEMPA*TEMPB/ALPEM IF ((X.NE.ZERO) .AND. (B(1).EQ.ZERO)) NCALC = 0 IF (NB .NE. 1) THEN IF (X .LE. ZERO) THEN DO 30 N=2,NB B(N) = ZERO 30 CONTINUE ELSE C--------------------------------------------------------------------- C Calculate higher order functions. C--------------------------------------------------------------------- TEMPC = HALFX TOVER = (ENMTEN+ENMTEN)/X IF (TEMPB.NE.ZERO) TOVER = ENMTEN/TEMPB DO 50 N=2,NB TEMPA = TEMPA/ALPEM ALPEM = ALPEM + ONE TEMPA = TEMPA*TEMPC IF (TEMPA.LE.TOVER*ALPEM) TEMPA = ZERO B(N) = TEMPA + TEMPA*TEMPB/ALPEM IF ((B(N).EQ.ZERO) .AND. (NCALC.GT.N)) 1 NCALC = N-1 50 CONTINUE END IF END IF ELSE IF ((X.GT.TWOFIV) .AND. (NB.LE.MAGX+1)) THEN C--------------------------------------------------------------------- C Asymptotic series for X .GT. 21.0. C--------------------------------------------------------------------- XC = SQRT(PI2/X) XIN = (EIGHTH/X)**2 M = 11 IF (X.GE.THREE5) M = 8 IF (X.GE.ONE30) M = 4 XM = FOUR*CONV(M) C--------------------------------------------------------------------- C Argument reduction for SIN and COS routines. C--------------------------------------------------------------------- T = AINT(X/(TWOPI1+TWOPI2)+HALF) Z = ((X-T*TWOPI1)-T*TWOPI2) - (ALPHA+HALF)/PI2 VSIN = SIN(Z) VCOS = COS(Z) GNU = ALPHA + ALPHA DO 80 I=1,2 S = ((XM-ONE)-GNU)*((XM-ONE)+GNU)*XIN*HALF T = (GNU-(XM-THREE))*(GNU+(XM-THREE)) CAPP = S*T/FACT(2*M+1) T1 = (GNU-(XM+ONE))*(GNU+(XM+ONE)) CAPQ = S*T1/FACT(2*M+2) XK = XM K = M + M T1 = T DO 70 J=2,M XK = XK - FOUR S = ((XK-ONE)-GNU)*((XK-ONE)+GNU) T = (GNU-(XK-THREE))*(GNU+(XK-THREE)) CAPP = (CAPP+ONE/FACT(K-1))*S*T*XIN CAPQ = (CAPQ+ONE/FACT(K))*S*T1*XIN K = K - 2 T1 = T 70 CONTINUE CAPP = CAPP + ONE CAPQ = (CAPQ+ONE)*(GNU*GNU-ONE)*(EIGHTH/X) B(I) = XC*(CAPP*VCOS-CAPQ*VSIN) IF (NB.EQ.1) GO TO 300 T = VSIN VSIN = -VCOS VCOS = T GNU = GNU + TWO 80 CONTINUE C--------------------------------------------------------------------- C If NB .GT. 2, compute J(X,ORDER+I) I = 2, NB-1 C--------------------------------------------------------------------- IF (NB .GT. 2) THEN GNU = ALPHA + ALPHA + TWO DO 90 J=3,NB B(J) = GNU*B(J-1)/X - B(J-2) GNU = GNU + TWO 90 CONTINUE END IF C--------------------------------------------------------------------- C Use recurrence to generate results. First initialize the C calculation of P*S. C--------------------------------------------------------------------- ELSE NBMX = NB - MAGX N = MAGX + 1 EN = CONV(N+N) + (ALPHA+ALPHA) PLAST = ONE P = EN/X C--------------------------------------------------------------------- C Calculate general significance test. C--------------------------------------------------------------------- TEST = ENSIG + ENSIG IF (NBMX .GE. 3) THEN C--------------------------------------------------------------------- C Calculate P*S until N = NB-1. Check for possible overflow. C--------------------------------------------------------------------- TOVER = ENTEN/ENSIG NSTART = MAGX + 2 NEND = NB - 1 EN = CONV(NSTART+NSTART) - TWO + (ALPHA+ALPHA) DO 130 K=NSTART,NEND N = K EN = EN + TWO POLD = PLAST PLAST = P P = EN*PLAST/X - POLD IF (P.GT.TOVER) THEN C--------------------------------------------------------------------- C To avoid overflow, divide P*S by TOVER. Calculate P*S until C ABS(P) .GT. 1. C--------------------------------------------------------------------- TOVER = ENTEN P = P/TOVER PLAST = PLAST/TOVER PSAVE = P PSAVEL = PLAST NSTART = N + 1 100 N = N + 1 EN = EN + TWO POLD = PLAST PLAST = P P = EN*PLAST/X - POLD IF (P.LE.ONE) GO TO 100 TEMPB = EN/X C--------------------------------------------------------------------- C Calculate backward test and find NCALC, the highest N such that C the test is passed. C--------------------------------------------------------------------- TEST = POLD*PLAST*(HALF-HALF/(TEMPB*TEMPB)) TEST = TEST/ENSIG P = PLAST*TOVER N = N - 1 EN = EN - TWO NEND = MIN(NB,N) DO 110 L=NSTART,NEND POLD = PSAVEL PSAVEL = PSAVE PSAVE = EN*PSAVEL/X - POLD IF (PSAVE*PSAVEL.GT.TEST) THEN NCALC = L - 1 GO TO 190 END IF 110 CONTINUE NCALC = NEND GO TO 190 END IF 130 CONTINUE N = NEND EN = CONV(N+N) + (ALPHA+ALPHA) C--------------------------------------------------------------------- C Calculate special significance test for NBMX .GT. 2. C--------------------------------------------------------------------- TEST = MAX(TEST,SQRT(PLAST*ENSIG)*SQRT(P+P)) END IF C--------------------------------------------------------------------- C Calculate P*S until significance test passes. C--------------------------------------------------------------------- 140 N = N + 1 EN = EN + TWO POLD = PLAST PLAST = P P = EN*PLAST/X - POLD IF (P.LT.TEST) GO TO 140 C--------------------------------------------------------------------- C Initialize the backward recursion and the normalization sum. C--------------------------------------------------------------------- 190 N = N + 1 EN = EN + TWO TEMPB = ZERO TEMPA = ONE/P M = 2*N - 4*(N/2) SUM = ZERO EM = CONV(N/2) ALPEM = (EM-ONE) + ALPHA ALP2EM = (EM+EM) + ALPHA IF (M .NE. 0) SUM = TEMPA*ALPEM*ALP2EM/EM NEND = N - NB IF (NEND .GT. 0) THEN C--------------------------------------------------------------------- C Recur backward via difference equation, calculating (but not C storing) B(N), until N = NB. C--------------------------------------------------------------------- DO 200 L=1,NEND N = N - 1 EN = EN - TWO TEMPC = TEMPB TEMPB = TEMPA TEMPA = (EN*TEMPB)/X - TEMPC M = 2 - M IF (M .NE. 0) THEN EM = EM - ONE ALP2EM = (EM+EM) + ALPHA IF (N.EQ.1) GO TO 210 ALPEM = (EM-ONE) + ALPHA IF (ALPEM.EQ.ZERO) ALPEM = ONE SUM = (SUM+TEMPA*ALP2EM)*ALPEM/EM END IF 200 CONTINUE END IF C--------------------------------------------------------------------- C Store B(NB). C--------------------------------------------------------------------- 210 B(N) = TEMPA IF (NEND .GE. 0) THEN IF (NB .LE. 1) THEN ALP2EM = ALPHA IF ((ALPHA+ONE).EQ.ONE) ALP2EM = ONE SUM = SUM + B(1)*ALP2EM GO TO 250 ELSE C--------------------------------------------------------------------- C Calculate and store B(NB-1). C--------------------------------------------------------------------- N = N - 1 EN = EN - TWO B(N) = (EN*TEMPA)/X - TEMPB IF (N.EQ.1) GO TO 240 M = 2 - M IF (M .NE. 0) THEN EM = EM - ONE ALP2EM = (EM+EM) + ALPHA ALPEM = (EM-ONE) + ALPHA IF (ALPEM.EQ.ZERO) ALPEM = ONE SUM = (SUM+B(N)*ALP2EM)*ALPEM/EM END IF END IF END IF NEND = N - 2 IF (NEND .NE. 0) THEN C--------------------------------------------------------------------- C Calculate via difference equation and store B(N), until N = 2. C--------------------------------------------------------------------- DO 230 L=1,NEND N = N - 1 EN = EN - TWO B(N) = (EN*B(N+1))/X - B(N+2) M = 2 - M IF (M .NE. 0) THEN EM = EM - ONE ALP2EM = (EM+EM) + ALPHA ALPEM = (EM-ONE) + ALPHA IF (ALPEM.EQ.ZERO) ALPEM = ONE SUM = (SUM+B(N)*ALP2EM)*ALPEM/EM END IF 230 CONTINUE END IF C--------------------------------------------------------------------- C Calculate B(1). C--------------------------------------------------------------------- B(1) = TWO*(ALPHA+ONE)*B(2)/X - B(3) 240 EM = EM - ONE ALP2EM = (EM+EM) + ALPHA IF (ALP2EM.EQ.ZERO) ALP2EM = ONE SUM = SUM + B(1)*ALP2EM C--------------------------------------------------------------------- C Normalize. Divide all B(N) by sum. C--------------------------------------------------------------------- 250 IF ((ALPHA+ONE).NE.ONE) 1 SUM = SUM*FUNC(ALPHA)*(X*HALF)**(-ALPHA) TEMPA = ENMTEN IF (SUM.GT.ONE) TEMPA = TEMPA*SUM DO 260 N=1,NB IF (ABS(B(N)).LT.TEMPA) B(N) = ZERO B(N) = B(N)/SUM 260 CONTINUE END IF C--------------------------------------------------------------------- C Error return -- X, NB, or ALPHA is out of range. C--------------------------------------------------------------------- ELSE B(1) = ZERO NCALC = MIN(NB,0) - 1 END IF C--------------------------------------------------------------------- C Exit C--------------------------------------------------------------------- 300 RETURN C ---------- Last line of RJBESL ---------- END