matlab代码无法进行并行计算

计算时报错“由于使用变量'A'的方式，Parfor无法运行”，求各位朋友帮忙看看代码问题出在哪里，代码如下：
clear;clc;close all
format long;
gxy=g*10^(-5);
%% 计算公式
[N,M]=size(gxy);
N1=35;
M1=35;
a(N1+1,M1+1)=0;
b(N1+1,M1+1)=0;
c(N1+1,M1+1)=0;
d(N1+1,M1+1)=0;
w1=pi/((N-1)/2);
w2=pi/((M-1)/2);
deltx=1850;
delty=1750;
gzz=zeros(N,M);
f=ones(N,M);
p=parpool(4);
for i=1:N
for j=1:M

    for m=0:N1
        for n=0:M1
            if(n==0);
                k1=2;
            else (n ~= 0);
                k1=1;
            end
        end
        if m==0;
            k2=2;
        else (m ~= 0);
            k2=1;
        end
    end
    a(n,m)=(1/(k1*k2*((N-1)/2)*((M-1)/2)))*sum(gxy(i,j)*cos(n*w1*deltx)*cos(n*w2*delty));
    b(n,m)=(1/(k1*k2*((N-1)/2)*((M-1)/2)))*sum(gxy(i,j)*sin(m*w1*deltx)*cos(n*w2*delty));
    c(n,m)=(1/(k1*k2*((N-1)/2)*((M-1)/2)))*sum(gxy(i,j)*cos(n*w1*deltx)*sin(m*w2*delty));
    d(n,m)=(1/(k1*k2*((N-1)/2)*((M-1)/2)))*sum(gxy(i,j)*sin(m*w1*deltx)*sin(m*w2*delty));
    gzz(i,j)=sqrt(n^2*(w1)^2+m^2*(w2)^2)*[cos(n*w1*f(i)) sin(m*w1*f(i))]...
        *[a(n,m) b(n,m);c(n,m) d(n,m)]* [cos(n*w2*f(j));sin(m*w2*f(j))]
end

end
gzz1=gzz*10^9;
delete(p);