function triangles(a0,b0,len0,delta,n)
%
%
% displaying a triangles.
%
for j=1:n
  a=a0+delta*(j-1);
  b=b0+delta*(j-1);
  len=len0-2*(j-1)*delta;
  x(1)=a;
  x(2)=x(1)+len;
  x(3)=x(2)-len/2.;
  x(4)=x(1);
  %--------------------
  y(1)=b;
  y(2)=y(1);
  y(3)=y(2)+len*sin(pi/3);
  y(4)=y(1);
%

  for i=1:3   
    line([x(i) x(i+1)],[y(i) y(i+1)]);
    text(x(i),y(i),num2str(i));
  end % i

end % j