Programmer 7500/MAX_PROGRAMMERS.iso/PASCAL/LN.ZIP/LN.INC

Text File | 1985-10-05 | 1.0 KB | 33 lines

{ ******************************************* }
{ *                                         * }
{ * The following is store as LN.INC        * }
{ *                                         * }
{ ******************************************* }


{ Turbo Pascal with BCD option does not support the ln function.          }

{ This used the taylor series expansion about x=1 to approximate ln(x).   }
{ ln(x):=                                                                 }
{   (1/1)*((x-1)^1) - (1/2)*((x-1)^2) + (1/3)*((x-1)^3) -                 }
{   (1/4)*((x-1)^4) + .. - (1/(n-1))*((x-1)^(n-1)) + (1/n)*((x-1)^n) - .. }

{ This expansion is valid for real values in the range 2>=x>0. }

function LN(X:real):real;
  var WorkTotal:real;
      term     :real;
      i        :integer;
  begin;
    term:=x - 1;
    WorkTotal:=term;
    for i:=2 to 25 do
      begin;
        term:=term * (x - 1)*(-1) / i;
        WorkTotal:=WorkTotal + term;
      end;
    ln:=WorkTotal;
  end;