帮忙看一下这三两行程序

[smart55427]

clc;
clear;
syms t k;
y=exp(-i*pi.*k*t);
fn=1/2*int(y,t,-0.5,0.5)
k=[-10:10];
stem(k,fn)


??? Error using ==> stem
The length of X must match the number of rows of Y.
Error in ==> ex3_4_1 at 7
stem(k,fn)

怎么改呢，求高手指点。