在command window 里面输入help sinc
SINC Sin(pi*x)/(pi*x) function.
SINC(X) returns a matrix whose elements are the sinc of the elements
of X, i.e.
y = sin(pi*x)/(pi*x) if x ~= 0
= 1 if x == 0
where x is an element of the input matrix and y is the resultant
output element.
% Example of a sinc function for a linearly spaced vector:
t = linspace(-5,5);
y = sinc(t);
plot(t,y);
xlabel('Time (sec)');ylabel('Amplitude'); title('Sinc Function')