求助关于积分问题

clc
clear
syms x y
a=12.24;
l=17.49;
k0=2*pi/l;
N=14;
l1=0.8;
gmn=zeros(1,N);
for ii=1:N
for jj=1:N
R=abs(jj-ii).*l/2+x./k0+y./k0;
u=@(y,x)cos(y*l/(4*l1))*exp(-j*k0*R)/(k0*R)
u1=dblquad(u,-0.2784,0.2784,-0.2784,0.2784)
gmn(1,ii)=gmn(1,ii)+u1;
end
end
编译老实通不过，各位高手给指点一下