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SUBROUTINE BESJ

PURPOSE
   COMPUTE THE J BESSEL FUNCTION FOR A GIVEN ARGUMENT AND ORDER

USAGE
   CALL BESJ(X,N,BJ,D,IER)

DESCRIPTION OF PARAMETERS
   X  -THE ARGUMENT OF THE J BESSEL FUNCTION DESIRED
   N  -THE ORDER OF THE J BESSEL FUNCTION DESIRED
   BJ -THE RESULTANT J BESSEL FUNCTION
   D  -REQUIRED ACCURACY
   IER-RESULTANT ERROR CODE WHERE
      IER=0  NO ERROR
      IER=1  N IS NEGATIVE
      IER=2  X IS NEGATIVE OR ZERO
      IER=3  REQUIRED ACCURACY NOT OBTAINED
      IER=4  RANGE OF N COMPARED TO X NOT CORRECT (SEE REMARKS)

REMARKS
   N MUST BE GREATER THAN OR EQUAL TO ZERO, BUT IT MUST BE
   LESS THAN
      20+10*X-X** 2/3	FOR X LESS THAN OR EQUAL TO 15
      90+X/2	       FOR X GREATER THAN 15

SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
   NONE

METHOD
   RECURRENCE RELATION TECHNIQUE DESCRIBED BY H. GOLDSTEIN AND
   R.M. THALER,'RECURRENCE TECHNIQUES FOR THE CALCULATION OF
   BESSEL FUNCTIONS',M.T.A.C.,V.13,PP.102-108 AND I.A. STEGUN
   AND M. ABRAMOWITZ,'GENERATION OF BESSEL FUNCTIONS ON HIGH
   SPEED COMPUTERS',M.T.A.C.,V.11,1957,PP.255-257