b=[19.97498333 39.94996666 19.97498333];
a=[68.2660915579 -0.0787823638 11.7126256859];
h=impz(b,a,10)
hold on; grid on;
plot(0:length(h)-1,h);
stem(0:length(h)-1,h);
axis([0,9,-0.2,0.6]);
hold off