%% Linear interpolation By L.R.Linares, 2007
%% It receives two points (x1, y1) and (x2, y2)
%% and the 'x' of a point for which we want to 
%% find the 'y'; I called this program 'XTOY'

<<
   "x1 x2 y1 y2 x" PROMPT
   -> x1 x2 y1 y2 x
   <<
      '(y2-y1)/(x2-x1)*(x-x1)+y1' EVAL
      x1 x2 y1 y2 5 ROLL
   >>
>>

---------------------------------------------
%% This other program is similar, but goes from
%% 'y' to 'x', I called it 'YTOX'.

<<
   "x1 x2 y1 y2 y" PROMPT
   -> x1 x2 y1 y2 y
   <<
      '(x2-x1)/(y2-y1)*(y-y1)+x1' EVAL
      x1 x2 y1 y2 5 ROLL
   >>
>>