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136 lines
5.8 KiB
Fortran
136 lines
5.8 KiB
Fortran
*DECK BESJ0
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FUNCTION BESJ0 (X)
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C***BEGIN PROLOGUE BESJ0
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C***PURPOSE Compute the Bessel function of the first kind of order
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C zero.
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C***LIBRARY SLATEC (FNLIB)
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C***CATEGORY C10A1
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C***TYPE SINGLE PRECISION (BESJ0-S, DBESJ0-D)
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C***KEYWORDS BESSEL FUNCTION, FIRST KIND, FNLIB, ORDER ZERO,
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C SPECIAL FUNCTIONS
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C***AUTHOR Fullerton, W., (LANL)
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C***DESCRIPTION
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C
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C BESJ0(X) calculates the Bessel function of the first kind of
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C order zero for real argument X.
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C
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C Series for BJ0 on the interval 0. to 1.60000D+01
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C with weighted error 7.47E-18
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C log weighted error 17.13
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C significant figures required 16.98
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C decimal places required 17.68
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C
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C Series for BM0 on the interval 0. to 6.25000D-02
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C with weighted error 4.98E-17
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C log weighted error 16.30
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C significant figures required 14.97
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C decimal places required 16.96
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C
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C Series for BTH0 on the interval 0. to 6.25000D-02
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C with weighted error 3.67E-17
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C log weighted error 16.44
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C significant figures required 15.53
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C decimal places required 17.13
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C
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C***REFERENCES (NONE)
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C***ROUTINES CALLED CSEVL, INITS, R1MACH, XERMSG
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C***REVISION HISTORY (YYMMDD)
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C 770401 DATE WRITTEN
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C 890210 REVISION DATE from Version 3.2
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
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C 900326 Removed duplicate information from DESCRIPTION section.
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C (WRB)
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C***END PROLOGUE BESJ0
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DIMENSION BJ0CS(13), BM0CS(21), BTH0CS(24)
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LOGICAL FIRST
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SAVE BJ0CS, BM0CS, BTH0CS, PI4, NTJ0, NTM0, NTTH0, XSML, XMAX,
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1 FIRST
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DATA BJ0CS( 1) / .1002541619 68939137E0 /
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DATA BJ0CS( 2) / -.6652230077 64405132E0 /
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DATA BJ0CS( 3) / .2489837034 98281314E0 /
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DATA BJ0CS( 4) / -.0332527231 700357697E0 /
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DATA BJ0CS( 5) / .0023114179 304694015E0 /
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DATA BJ0CS( 6) / -.0000991127 741995080E0 /
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DATA BJ0CS( 7) / .0000028916 708643998E0 /
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DATA BJ0CS( 8) / -.0000000612 108586630E0 /
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DATA BJ0CS( 9) / .0000000009 838650793E0 /
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DATA BJ0CS(10) / -.0000000000 124235515E0 /
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DATA BJ0CS(11) / .0000000000 001265433E0 /
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DATA BJ0CS(12) / -.0000000000 000010619E0 /
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DATA BJ0CS(13) / .0000000000 000000074E0 /
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DATA BM0CS( 1) / .0928496163 7381644E0 /
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DATA BM0CS( 2) / -.0014298770 7403484E0 /
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DATA BM0CS( 3) / .0000283057 9271257E0 /
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DATA BM0CS( 4) / -.0000014330 0611424E0 /
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DATA BM0CS( 5) / .0000001202 8628046E0 /
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DATA BM0CS( 6) / -.0000000139 7113013E0 /
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DATA BM0CS( 7) / .0000000020 4076188E0 /
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DATA BM0CS( 8) / -.0000000003 5399669E0 /
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DATA BM0CS( 9) / .0000000000 7024759E0 /
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DATA BM0CS(10) / -.0000000000 1554107E0 /
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DATA BM0CS(11) / .0000000000 0376226E0 /
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DATA BM0CS(12) / -.0000000000 0098282E0 /
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DATA BM0CS(13) / .0000000000 0027408E0 /
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DATA BM0CS(14) / -.0000000000 0008091E0 /
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DATA BM0CS(15) / .0000000000 0002511E0 /
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DATA BM0CS(16) / -.0000000000 0000814E0 /
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DATA BM0CS(17) / .0000000000 0000275E0 /
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DATA BM0CS(18) / -.0000000000 0000096E0 /
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DATA BM0CS(19) / .0000000000 0000034E0 /
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DATA BM0CS(20) / -.0000000000 0000012E0 /
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DATA BM0CS(21) / .0000000000 0000004E0 /
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DATA BTH0CS( 1) / -.2463916377 4300119E0 /
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DATA BTH0CS( 2) / .0017370983 07508963E0 /
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DATA BTH0CS( 3) / -.0000621836 33402968E0 /
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DATA BTH0CS( 4) / .0000043680 50165742E0 /
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DATA BTH0CS( 5) / -.0000004560 93019869E0 /
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DATA BTH0CS( 6) / .0000000621 97400101E0 /
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DATA BTH0CS( 7) / -.0000000103 00442889E0 /
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DATA BTH0CS( 8) / .0000000019 79526776E0 /
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DATA BTH0CS( 9) / -.0000000004 28198396E0 /
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DATA BTH0CS(10) / .0000000001 02035840E0 /
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DATA BTH0CS(11) / -.0000000000 26363898E0 /
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DATA BTH0CS(12) / .0000000000 07297935E0 /
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DATA BTH0CS(13) / -.0000000000 02144188E0 /
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DATA BTH0CS(14) / .0000000000 00663693E0 /
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DATA BTH0CS(15) / -.0000000000 00215126E0 /
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DATA BTH0CS(16) / .0000000000 00072659E0 /
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DATA BTH0CS(17) / -.0000000000 00025465E0 /
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DATA BTH0CS(18) / .0000000000 00009229E0 /
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DATA BTH0CS(19) / -.0000000000 00003448E0 /
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DATA BTH0CS(20) / .0000000000 00001325E0 /
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DATA BTH0CS(21) / -.0000000000 00000522E0 /
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DATA BTH0CS(22) / .0000000000 00000210E0 /
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DATA BTH0CS(23) / -.0000000000 00000087E0 /
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DATA BTH0CS(24) / .0000000000 00000036E0 /
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DATA PI4 / 0.7853981633 9744831E0 /
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DATA FIRST /.TRUE./
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C***FIRST EXECUTABLE STATEMENT BESJ0
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IF (FIRST) THEN
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NTJ0 = INITS (BJ0CS, 13, 0.1*R1MACH(3))
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NTM0 = INITS (BM0CS, 21, 0.1*R1MACH(3))
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NTTH0 = INITS (BTH0CS, 24, 0.1*R1MACH(3))
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C
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XSML = SQRT (8.0*R1MACH(3))
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XMAX = 1.0/R1MACH(4)
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ENDIF
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FIRST = .FALSE.
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C
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Y = ABS(X)
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IF (Y.GT.4.0) GO TO 20
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C
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BESJ0 = 1.0
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IF (Y.GT.XSML) BESJ0 = CSEVL (.125*Y*Y-1., BJ0CS, NTJ0)
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RETURN
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C
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20 IF (Y .GT. XMAX) CALL XERMSG ('SLATEC', 'BESJ0',
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+ 'NO PRECISION BECAUSE ABS(X) IS TOO BIG', 1, 2)
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C
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Z = 32.0/Y**2 - 1.0
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AMPL = (0.75 + CSEVL (Z, BM0CS, NTM0)) / SQRT(Y)
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THETA = Y - PI4 + CSEVL (Z, BTH0CS, NTTH0) / Y
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BESJ0 = AMPL * COS (THETA)
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C
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RETURN
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END
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