matlab：Error using ==> mtimes Inner matrix dimensions must a

matlab：Error using ==> mtimes Inner matrix dimensions must agree.
我有一个matlab程序：
clc
clear
fc=300;
fs=1000;
nn=512;
wn=2*fc/fs;
n=40;
a1=(n-1)/2;
m=ceil(wn*n/2);
absh=[ones(1,m),zeros(1,n-2*m+1),ones(1,m-1)];
k1=0:ceil((n-1)/2);
k2=ceil((n-1)/2+1:n-1);
angleh=[-a1*(2*pi)/n*k1,a1*(2*pi)/n*(n-k2)];
h=absh*exp(i*angleh);
b=real(ifft(h));
freqz(b,1,nn,fs)
运行后出现错误：Error using ==> mtimes
Inner matrix dimensions must agree.
毕业设计急用.