You can run Tbessy for an example where N = 2 and X = 0.75 or you can call BESSY(N,X) directly with your own values.
Code:
//************************************************************************
//* *
//* Program to calculate the second kind Bessel function of integer *
//* order N, for any REAL X, using the function BESSY(N,X). *
//* *
//* -------------------------------------------------------------------- *
//* *
//* SAMPLE RUN: *
//* *
//* (Calculate Bessel function for N:=2, X:=0.75). *
//* *
//* Second kind Bessel function of order 2 for X = 0.7500: *
//* *
//* Y := -2.62974604 *
//* *
//* -------------------------------------------------------------------- *
//* Reference: From Numath Library By Tuan Dang Trong in Fortran 77. *
//* *
//* C++ Release 1.0 By J-P Moreau, Paris. *
//* (www.jpmoreau.fr) *
//* Translated to HPPL by Tom Lake *
//***********************************************************************/
BESSJ0 (X)
BEGIN
//***********************************************************************
// This subroutine calculates the First Kind Bessel Function of
// order 0, for any real number X. The polynomial approximation by
// series of Chebyshev polynomials is used for 0<X<8 and 0<8/X<1.
// REFERENCES:
// M.ABRAMOWITZ,I.A.STEGUN, HANDBOOK OF MATHEMATICAL FUNCTIONS, 1965.
// C.W.CLENSHAW, NATIONAL PHYSICAL LABORATORY MATHEMATICAL TABLES,
// VOL.5, 1962.
//************************************************************************/
LOCAL P1:=1.0, P2:=-0.1098628627E-2, P3:=0.2734510407E-4;
LOCAL P4:=-0.2073370639E-5, P5:= 0.2093887211E-6;
LOCAL Q1:=-0.1562499995E-1, Q2:= 0.1430488765E-3, Q3:=-0.6911147651E-5;
LOCAL Q4:= 0.7621095161E-6, Q5:=-0.9349451520E-7;
LOCAL R1:= 57568490574.0, R2:=-13362590354.0, R3:=651619640.7;
LOCAL R4:=-11214424.18, R5:= 77392.33017, R6:=-184.9052456;
LOCAL S1:= 57568490411.0, S2:=1029532985.0, S3:=9494680.718;
LOCAL S4:= 59272.64853, S5:=267.8532712, S6:=1.0;
LOCAL AX,FR,FS,Z,FP1,FQ,XX,Y;
LOCAL TMP;
IF (X==0.0) THEN RETURN 1.0; END;
AX := ABS(X);
IF (AX < 8.0) THEN
Y := X*X;
FR := R1+Y*(R2+Y*(R3+Y*(R4+Y*(R5+Y*R6))));
FS := S1+Y*(S2+Y*(S3+Y*(S4+Y*(S5+Y*S6))));
TMP := FR/FS;
ELSE
Z := 8./AX;
Y := Z*Z;
XX := AX-0.785398164;
FP1 := P1+Y*(P2+Y*(P3+Y*(P4+Y*P5)));
FQ := Q1+Y*(Q2+Y*(Q3+Y*(Q4+Y*Q5)));
TMP := SQRT(0.636619772/AX)*(FP1*COS(XX)-Z*FQ*SIN(XX));
END;
RETURN TMP;
END;
Signu (X,Y)
BEGIN
IF (Y<0.0) THEN
RETURN (-ABS(X));
ELSE
RETURN (ABS(X));
END;
END;
BESSJ1 (X)
BEGIN
//**********************************************************************
// This subroutine calculates the First Kind Bessel Function of
// order 1, for any real number X. The polynomial approximation by
// series of Chebyshev polynomials is used for 0<X<8 and 0<8/X<1.
// REFERENCES:
// M.ABRAMOWITZ,I.A.STEGUN, HANDBOOK OF MATHEMATICAL FUNCTIONS, 1965.
// C.W.CLENSHAW, NATIONAL PHYSICAL LABORATORY MATHEMATICAL TABLES,
// VOL.5, 1962.
//***********************************************************************/
LOCAL P1:=1.0, P2:=0.183105E-2, P3:=-0.3516396496E-4, P4:=0.2457520174E-5;
LOCAL P5:=-0.240337019E-6, P6:=0.636619772;
LOCAL Q1:= 0.04687499995, Q2:=-0.2002690873E-3, Q3:=0.8449199096E-5;
LOCAL Q4:=-0.88228987E-6, Q5:= 0.105787412E-6;
LOCAL R1:= 72362614232.0, R2:=-7895059235.0, R3:=242396853.1;
LOCAL R4:=-2972611.439, R5:=15704.48260, R6:=-30.16036606;
LOCAL S1:=144725228442.0, S2:=2300535178.0, S3:=18583304.74;
LOCAL S4:=99447.43394, S5:=376.9991397, S6:=1.0;
LOCAL AX,FR,FS,Y,Z,FP1,FQ,XX;
LOCAL TMP;
AX := ABS(X);
IF (AX < 8.0) THEN
Y := X*X;
FR := R1+Y*(R2+Y*(R3+Y*(R4+Y*(R5+Y*R6))));
FS := S1+Y*(S2+Y*(S3+Y*(S4+Y*(S5+Y*S6))));
TMP := X*(FR/FS);
ELSE
Z := 8.0/AX;
Y := Z*Z;
XX := AX-2.35619491;
FP1 := P1+Y*(P2+Y*(P3+Y*(P4+Y*P5)));
FQ := Q1+Y*(Q2+Y*(Q3+Y*(Q4+Y*Q5)));
TMP := SQRT(P6/AX)*(COS(XX)*FP1-Z*SIN(XX)*FQ)*Signu(S6,X);
END;
RETURN TMP;
END;
BESSY0(X)
BEGIN
//* --------------------------------------------------------------------
// This subroutine calculates the Second Kind Bessel Function of
// order 0, for any real number X. The polynomial approximation by
// series of Chebyshev polynomials is used for 0<X<8 and 0<8/X<1.
// REFERENCES:
// M.ABRAMOWITZ,I.A.STEGUN, HANDBOOK OF MATHEMATICAL FUNCTIONS, 1965.
// C.W.CLENSHAW, NATIONAL PHYSICAL LABORATORY MATHEMATICAL TABLES,
// VOL.5, 1962.
// --------------------------------------------------------------------- */
LOCAL P1:= 1.0, P2:=-0.1098628627E-2, P3:=0.2734510407E-4;
LOCAL P4:=-0.2073370639E-5, P5:= 0.2093887211E-6;
LOCAL Q1:=-0.1562499995E-1, Q2:= 0.1430488765E-3, Q3:=-0.6911147651E-5;
LOCAL Q4:= 0.7621095161E-6, Q5:=-0.9349451520E-7;
LOCAL R1:=-2957821389.0, R2:=7062834065.0, R3:=-512359803.6;
LOCAL R4:= 10879881.29, R5:=-86327.92757, R6:=228.4622733;
LOCAL S1:= 40076544269.0, S2:=745249964.8, S3:=7189466.438;
LOCAL S4:= 47447.26470, S5:=226.1030244, S6:=1.0;
LOCAL FS,FR,Z,FP1,FQ,XX,Y;
IF (X == 0.0) THEN RETURN -1e30; END;
IF (X < 8.0) THEN
Y := X*X;
FR := R1+Y*(R2+Y*(R3+Y*(R4+Y*(R5+Y*R6))));
FS := S1+Y*(S2+Y*(S3+Y*(S4+Y*(S5+Y*S6))));
RETURN (FR/FS+0.636619772*BESSJ0(X)*LN(X));
ELSE
Z := 8.0/X;
Y := Z*Z;
XX := X-0.785398164;
FP1 := P1+Y*(P2+Y*(P3+Y*(P4+Y*P5)));
FQ := Q1+Y*(Q2+Y*(Q3+Y*(Q4+Y*Q5)));
RETURN (SQRT(0.636619772/X)*(FP1*SIN(XX)+Z*FQ*COS(XX)));
END;
END;
BESSY1(X)
BEGIN
//* ---------------------------------------------------------------------
// This subroutine calculates the Second Kind Bessel Function of
// order 1, for any real number X. The polynomial approximation by
// series of Chebyshev polynomials is used for 0<X<8 and 0<8/X<1.
// REFERENCES:
// M.ABRAMOWITZ,I.A.STEGUN, HANDBOOK OF MATHEMATICAL FUNCTIONS, 1965.
// C.W.CLENSHAW, NATIONAL PHYSICAL LABORATORY MATHEMATICAL TABLES,
// VOL.5, 1962.
// ---------------------------------------------------------------------- */
LOCAL P1:= 1.0, P2:=0.183105E-2, P3:=-0.3516396496E-4;
LOCAL P4:= 0.2457520174E-5, P5:=-0.240337019E-6;
LOCAL Q1:= 0.04687499995, Q2:=-0.2002690873E-3, Q3:=0.8449199096E-5;
LOCAL Q4:=-0.88228987E-6, Q5:= 0.105787412E-6;
LOCAL R1:=-0.4900604943E13, R2:= 0.1275274390E13, R3:=-0.5153438139E11;
LOCAL R4:= 0.7349264551E9, R5:=-0.4237922726E7, R6:= 0.8511937935E4;
LOCAL S1:= 0.2499580570E14, S2:= 0.4244419664E12, S3:= 0.3733650367E10;
LOCAL S4:= 0.2245904002E8, S5:= 0.1020426050E6, S6:= 0.3549632885E3, S7:=1.0;
LOCAL FR,FS,Z,FP1,FQ,XX, Y;
IF (X == 0.0) THEN RETURN -1e30; END;
IF (X < 8.0) THEN
Y := X*X;
FR := R1+Y*(R2+Y*(R3+Y*(R4+Y*(R5+Y*R6))));
FS := S1+Y*(S2+Y*(S3+Y*(S4+Y*(S5+Y*(S6+Y*S7)))));
RETURN (X*(FR/FS)+0.636619772*(BESSJ1(X)*LN(X)-1.0/X));
ELSE
Z := 8./X;
Y := Z*Z;
XX := X-2.356194491;
FP1 := P1+Y*(P2+Y*(P3+Y*(P4+Y*P5)));
FQ := Q1+Y*(Q2+Y*(Q3+Y*(Q4+Y*Q5)));
RETURN (SQRT(0.636619772/X)*(SIN(XX)*FP1+Z*COS(XX)*FQ));
END;
END;
EXPORT BESSY(N,X)
BEGIN
//* -----------------------------------------------------------------
// This subroutine calculates the second kind Bessel Function of
// integer order N, for any real X. We use here the classical
// recursive formula.
// ------------------------------------------------------------------ */
LOCAL TOX,BY,BYM,BYP,J;
IF (N == 0) THEN RETURN BESSY0(X); END;
IF (N == 1) THEN RETURN BESSY1(X); END;
IF (X == 0.0) THEN RETURN -1e30; END;
TOX := 2.0/X;
BY := BESSY1(X);
BYM := BESSY0(X);
FOR J:=1 TO N-1 DO
BYP := J*TOX*BY-BYM;
BYM := BY;
BY := BYP;
END;
RETURN BY;
END;
// --------------------------------------------------------------------------
BESSYP(N,X)
BEGIN
IF (N == 0) THEN
RETURN (-BESSY(1,X));
ELSE
IF (X == 0.0) THEN
RETURN 1e-30;
ELSE
RETURN (BESSY(N-1,X)-(1.0*N/X)*BESSY(N,X));
END;
END;
END;
EXPORT Tbessy()
BEGIN
LOCAL X,Y,N;
N:=2;
X:=0.75;
Y := BESSY(N,X);
PRINT("\n Second Kind Bessel Function of order " + N + ", for X= " + X + "\n\n");
PRINT(" Y = "+CAS(format(Y,"s9"))+"\n\n");
END;
// End of file Tbessy.hpprgm
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