%%%%%%%%%%%%%%%%%%%%% Reflection in a triangle side %%%%%%%%%%%%%%%%%%%%%
%
% TRIREFL
% Usage: TRIREFL(tri,side)
% Inputs:  tri - a vector who components are the vertices of a triangle 
%          side -  the side of the triangle in which to reflect
%          side must be one of 'a', 'b' or 'c'  or 'A' 'B' or 'C' 
%          the upper case designation is used to denote a reflection 
%          whwere the resulting tiangle is not drawn
%          
% Output: vertices of the reflected triangle
%         
%     if [A, B, C] are the vertices and a, b, c are the opposite sides
%     then action is as follows:
%
%     reflecting side       fixed vertices      changed vertex               
%          
%            a                 C, B                   A
%            b                 A, C                   B
%            c                 A, B                   C

function T  = trirefl(tri,side)
    
    if (side == 'a')|(side == 'A')   perm = [3 2 1]; end;
    if (side == 'b')|(side == 'B')   perm = [1 3 2]; end;        
    if (side == 'c')|(side == 'C')   perm = [1 2 3]; end;
    tri = tri(perm); 
    P = tri(1,1); 
    Q = tri(1,2); 
    R = tri(1,3); 
    R = reflect([P Q],R);
    T = [P Q R];
    T = T(perm);