Octave / line_interp

function y1 = line_interp (x, y, new_x)
  y1 = [];
  for i = 1 : length(new_x)
    k = 2;
    while (new_x(i) > x(k))
      k += 1;
    endwhile
    a = (y(k) - y(k-1))/(x(k) - x(k-1));
    b = y(k-1) - a * x(k-1);
    res = @(x) a * x + b;
    y1 = [y1, res(new_x(i))];
  endfor
endfunction