How the numerator be formed for causal LTI system

Hi I have made the code for non causal system but according to figure, I want modification in the code clf; n=-29:1:31; N=61; x=[zeros(1,24),1.5,3,1,0,-0.5,2,-0.5,0,1,3,1.5,zeros(1,26)]; num=[5 0 1.66 0 0 0.5]; den=[1 0 -0.5 0 0.25 0]; h=impz(num,den,N); y=conv(x,h); stem(n,y);

 for non causal system