MATLAB: Plot Problem

plotting

These commands create the expected plot:

x=.1:.1:4*pi;
y=sin(pi*x)/pi;
plot(x,y)

However, the following commands create a horizontal line at zero:

x=.1:.1:4*pi;
y=(sin(pi*x))/(pi*x);
plot(x,y)

(I don't have a sinc function.) I don't understand why the second set of commands doesn't work. Thoughts?

You are using mrdivide when you want to use rdivide

x = -20:0.0001:20;
y = (sin(pi*x))./(pi*x);
y(x==0) = 1;% If you don't get: (Warning: Divide by zero.) you missed 0.
plot(x,y)

y = (P./x).*sin(x) + cos(x);