  function [xmax]=max3(x1,x2,x3)
%
% From Chapter 2, "Linear Advection Equation", of the book: 
% Graham W Griffiths and William E Schiesser (2011).
% Traveling Wave Analysis of Partial Differential Equations
% - Numerical and Analytical Methods with Matlab and Maple,
% Academic Press (ISBN: 9780123846525).
% 
  xmax=x1;
  if(x2 > x1)xmax=x2; end
  if(x3 > xmax)xmax=x3; end

