program Project1;

uses
  SysUtils,
  spe,
  MathUnit;


const
  w = 15;
// Numerical recipes

function gammln(x: double): Double;
{ gibt den Log der vollständigen Gamma-Funktion zurück (x>0).
     Gamma(x) = integral ( t^(x-1) * exp(-t) dt ) (von 0 bis Unendlich)
  (Log, um Floating Point Underflow zu vermeiden). }
const
  stp  = 2.50662827465;
var
  xx,tmp,ser : extended;
begin
  if x<=0 then
    raise Exception.Create('Argument für GammaLn ist negativ.');
  if (x>1) then begin
    xx  := x  - 1.0;
    tmp := xx + 5.5;
    tmp := (xx+0.5) * ln(tmp) - tmp;
    ser := 1.0 + 76.18009173    /(xx+1.0) - 86.50532033/(xx+2.0)
               + 24.01409822    /(xx+3.0) - 1.231739516/(xx+4.0)
               +  0.120858003E-2/(xx+5.0) - 0.536382E-5/(xx+6.0);
    result := tmp + ln(stp*ser);
  end else
  if (x<1) then
    result := GammaLn(x+1.0) - ln(x)
  else
  if (x=1) then
    result := 0.0;
end;

function Beta(a,b: Double) : Double;
begin
  Result := exp(gammln(a) + gammln(b) - gammln(a+b));
end;

procedure Test(a, b: Double);
var
  y_lazStats, y_numlib, y_numrecip: Double;
begin
  y_numlib := spe.beta(a, b);
  y_lazstats := mathunit.beta(a, b);
  y_numrecip := beta(a, b);
  WriteLn(a:w:5, b:w:5, y_lazstats:w:5, y_numlib:w:5, y_numrecip:w:5);
end;

begin
  WriteLn('Beta function');
  WriteLn;
  WriteLn('a':w, 'b':w, 'y(lazstats)':w, 'y(numlib)':w, 'y(Num.Recip)':w);
  Test(0.5, 0.5);
  Test(1.1, 2.3);
  Test(2.3, 1.1);
  Test(2.9, 0.1);
  Test(5.1, 2.5);
  ReadLn;
end.