UNIT C_Rect;

INTERFACE

TYPE Func=Function(x:real):real;

FUNCTION  Rectangles(a,b:Real; f:Func; n:word):Real;
FUNCTION RectanglesRunge(a,b:Real; f:Func; var n: word;eps:Real):Real;

IMPLEMENTATION

FUNCTION  Rectangles(a,b:Real; f:Func; n:word):Real;

VAR
  h,f1,sum,x,y:Real;
  i:Integer;

BEGIN

  h := (b-a) / n;
  sum := 0;
  x := a;
  for i := 1 to n  do
     begin
       y := x;
       x := x + h;
       f1 := f((x + y)/2);
       sum := sum + f1;
     end;
  Rectangles:= sum*h;
END;

FUNCTION RectanglesRunge(a,b:Real; f:Func; var n: word; eps:Real):Real;

VAR
  I1, I2: real;
BEGIN
   I1 := Rectangles(a,b,f,n);
   n := n+n;
   I2 := Rectangles(a,b,f,n);
   while abs(I1-I2)>2*eps do
     begin
       if n >=  16383 then break;
       I1 := I2;
       n := n+n;
       I2 := Rectangles(a,b,f,n);
     end;
  RectanglesRunge := I2;
END;

BEGIN
END.