C I0 10
C ..................................................................I0 20
C I0 30
C SUBROUTINE I0 I0 40
C I0 50
C PURPOSE I0 60
C COMPUTE THE MODIFIED BESSEL FUNCTION I OF ORDER ZERO I0 70
C I0 80
C USAGE I0 90
C CALL I0(X,RI0) I0 100
C I0 110
C DESCRIPTION OF PARAMETERS I0 120
C X -GIVEN ARGUMENT OF THE BESSEL FUNCTION I OF ORDER 0 I0 130
C RI0 -RESULTANT VALUE OF THE BESSEL FUNCTION I OF ORDER 0 I0 140
C I0 150
C REMARKS I0 160
C LARGE VALUES OF THE ARGUMENT MAY CAUSE OVERFLOW IN THE I0 170
C BUILTIN EXP-FUNCTION I0 180
C I0 190
C SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED I0 200
C NONE I0 210
C I0 220
C METHOD I0 230
C POLYNOMIAL APPROXIMATIONS GIVEN BY E.E. ALLEN ARE USED FOR I0 240
C CALCULATION. I0 250
C FOR REFERENCE SEE I0 260
C M. ABRAMOWITZ AND I.A. STEGUN,'HANDBOOK OF MATHEMATICAL I0 270
C FUNCTIONS', U.S. DEPARTMENT OF COMMERCE, NATIONAL BUREAU OF I0 280
C STANDARDS APPLIED MATHEMATICS SERIES, 1966, P.378. I0 290
C I0 300
C ..................................................................I0 310
C I0 320
SUBROUTINE I0(X,RI0) I0 330
RI0=ABS(X) I0 340
IF(RI0-3.75)1,1,2 I0 350
1 Z=X*X*7.111111E-2 I0 360
RI0=((((( 4.5813E-3*Z+3.60768E-2)*Z+2.659732E-1)*Z+1.206749E0)*Z I0 370
1+3.089942E0)*Z+3.515623E0)*Z+1. I0 380
RETURN I0 390
2 Z=3.75/RI0 I0 400
RI0= EXP(RI0)/SQRT(RI0)*((((((((3.92377E-3*Z-1.647633E-2)*Z I0 410
1+2.635537E-2)*Z-2.057706E-2)*Z+9.16281E-3)*Z-1.57565E-3)*Z I0 420
2+2.25319E-3)*Z+1.328592E-2)*Z+3.989423E-1) I0 430
RETURN I0 440
END I0 450