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83 lines
3.5 KiB
Fortran
83 lines
3.5 KiB
Fortran
*DECK DBESI1
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DOUBLE PRECISION FUNCTION DBESI1 (X)
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C***BEGIN PROLOGUE DBESI1
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C***PURPOSE Compute the modified (hyperbolic) Bessel function of the
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C first kind of order one.
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C***LIBRARY SLATEC (FNLIB)
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C***CATEGORY C10B1
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C***TYPE DOUBLE PRECISION (BESI1-S, DBESI1-D)
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C***KEYWORDS FIRST KIND, FNLIB, HYPERBOLIC BESSEL FUNCTION,
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C MODIFIED BESSEL FUNCTION, ORDER ONE, 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 DBESI1(X) calculates the double precision modified (hyperbolic)
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C Bessel function of the first kind of order one and double precision
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C argument X.
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C
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C Series for BI1 on the interval 0. to 9.00000E+00
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C with weighted error 1.44E-32
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C log weighted error 31.84
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C significant figures required 31.45
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C decimal places required 32.46
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C
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C***REFERENCES (NONE)
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C***ROUTINES CALLED D1MACH, DBSI1E, DCSEVL, INITDS, XERMSG
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C***REVISION HISTORY (YYMMDD)
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C 770701 DATE WRITTEN
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C 890531 Changed all specific intrinsics to generic. (WRB)
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C 890531 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***END PROLOGUE DBESI1
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DOUBLE PRECISION X, BI1CS(17), XMAX, XMIN, XSML, Y, D1MACH,
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1 DCSEVL, DBSI1E
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LOGICAL FIRST
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SAVE BI1CS, NTI1, XMIN, XSML, XMAX, FIRST
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DATA BI1CS( 1) / -.1971713261 0998597316 1385032181 49 D-2 /
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DATA BI1CS( 2) / +.4073488766 7546480608 1553936520 14 D+0 /
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DATA BI1CS( 3) / +.3483899429 9959455866 2450377837 87 D-1 /
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DATA BI1CS( 4) / +.1545394556 3001236038 5984010584 89 D-2 /
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DATA BI1CS( 5) / +.4188852109 8377784129 4588320041 20 D-4 /
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DATA BI1CS( 6) / +.7649026764 8362114741 9597039660 69 D-6 /
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DATA BI1CS( 7) / +.1004249392 4741178689 1798080372 38 D-7 /
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DATA BI1CS( 8) / +.9932207791 9238106481 3712980548 63 D-10 /
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DATA BI1CS( 9) / +.7663801791 8447637275 2001716813 49 D-12 /
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DATA BI1CS( 10) / +.4741418923 8167394980 3880919481 60 D-14 /
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DATA BI1CS( 11) / +.2404114404 0745181799 8631720320 00 D-16 /
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DATA BI1CS( 12) / +.1017150500 7093713649 1211007999 99 D-18 /
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DATA BI1CS( 13) / +.3645093565 7866949458 4917333333 33 D-21 /
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DATA BI1CS( 14) / +.1120574950 2562039344 8106666666 66 D-23 /
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DATA BI1CS( 15) / +.2987544193 4468088832 0000000000 00 D-26 /
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DATA BI1CS( 16) / +.6973231093 9194709333 3333333333 33 D-29 /
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DATA BI1CS( 17) / +.1436794822 0620800000 0000000000 00 D-31 /
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DATA FIRST /.TRUE./
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C***FIRST EXECUTABLE STATEMENT DBESI1
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IF (FIRST) THEN
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NTI1 = INITDS (BI1CS, 17, 0.1*REAL(D1MACH(3)))
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XMIN = 2.0D0*D1MACH(1)
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XSML = SQRT(4.5D0*D1MACH(3))
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XMAX = LOG (D1MACH(2))
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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.3.0D0) GO TO 20
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C
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DBESI1 = 0.D0
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IF (Y.EQ.0.D0) RETURN
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C
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IF (Y .LE. XMIN) CALL XERMSG ('SLATEC', 'DBESI1',
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+ 'ABS(X) SO SMALL I1 UNDERFLOWS', 1, 1)
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IF (Y.GT.XMIN) DBESI1 = 0.5D0*X
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IF (Y.GT.XSML) DBESI1 = X*(0.875D0 + DCSEVL (Y*Y/4.5D0-1.D0,
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1 BI1CS, NTI1))
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RETURN
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C
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20 IF (Y .GT. XMAX) CALL XERMSG ('SLATEC', 'DBESI1',
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+ 'ABS(X) SO BIG I1 OVERFLOWS', 2, 2)
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C
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DBESI1 = EXP(Y) * DBSI1E(X)
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C
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RETURN
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END
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