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Pascal/Delphi Source File  |  1991-04-29  |  552 b   |  17 lines
  1. FUNCTION bessi0(x: real): real;
  2. VAR
  3.    ax: real;  y,ans: double;
  4. BEGIN
  5.    IF (abs(x) < 3.75) THEN BEGIN
  6.       y := sqr(x/3.75);
  7.       ans := 1.0+y*(3.5156229+y*(3.0899424+y*(1.2067492+y*
  8.          (0.2659732+y*(0.360768e-1+y*0.45813e-2)))))  END
  9.    ELSE BEGIN
  10.       ax := abs(x);  y := 3.75/ax;
  11.       ans := (exp(ax)/sqrt(ax))*(0.39894228+y*(0.1328592e-1
  12.          +y*(0.225319e-2+y*(-0.157565e-2+y*(0.916281e-2
  13.          +y*(-0.2057706e-1+y*(0.2635537e-1+y*(-0.1647633e-1
  14.          +y*0.392377e-2))))))))  END;
  15.    bessi0 := sngl(ans)
  16. END;
  17.