Computing a convolution sum with MATLAB

Let
x[n]=u[n-1]-u[n-1] and h[n]=tri((n-6)/4). Find the convolution sum x[n]*h[n] using MATALB CONVOLUTION and x[n]  is limited to range 1 and 5 , h[n] is limited to range 3 and 9.

script for above one's

nx = -2:8 ; nh = 0:12;              % Set time vectors for x and h
x = usD(n-1) - usD(n-6);            % Compute values of x
h = tri((nh-6)/4);                  % Compute values of h
y = conv(x,h);                      % Compute the convolution of x with h
                                    %
                                    % Generate a discrete-time vector for y
                                    %
ny = (nx(1) + nh(1)) + (0:(length(nx) + length(nh) - 2)) ;
                                    %
                                    % Graph the results
                                    %
subplot(3,1,1) ; stem(nx,x,'k', 'filled');
xlabel('n') ; ylabel('x'); axis([-2,20,0,4]);
subplot(3,1,2) ; stem(nh,h,'k','filled') ;
xlabel('n') ; ylabel('h'); axis([-2,20,0,4]);
subplot(3,1,3) ; stem(ny,y,'k','filled');
xlabel('n') ; ylabel('y'); axis([-2,20,0,4]);

and functions for unit step discrete "usD" and "tri"
Tri function.

%  Function to compute the triangle function.  Uses the definition
%  of the triangle function in terms of the ramp function.  Works
%  for vectors and scalars equally well.

function y = tri(t)
  y = ramp(t+1) - 2*ramp(t) + ramp(t-1) ;

usD function

%  Unit sequence function defined as 0 for input integer argument 
%  values less than zero, and 1 for input integer argument values 
%  equal to or greater than zero.  Returns "NaN" for non-integer 
%  arguments.  Works for vectors and scalars equally well.
%
%  function y = uD(n)

function y = usD(n)
  y = double(n >= 0) ;    %  Set output to one for non-
          %  negative arguments
  ss = find(round(n)~=n) ;  %  Find all non-integer "n's"
  y(ss) = NaN ;      %  Set the corresponding outputs 
          %  all to "NaN"

And please help I cannot get any graph with above one script and two functions i.e usD and tri function.Do i need to keep convolution "conv" function y = conv(x,h); also? please give me conv function else

please give me suggestion for the above mat lab program to execute and I want to get graph for it???