Problem solving DE neural network

Hi,

I need a help with this solution expecially with the last line mesh(x1,x2,y). Error: Unrecognized function or variable 'x1' and 'x2'

clear all

load zad2.mat

k=1; n=length(x);

for i=1:n

for j=1:n

z(i,j)=u(i,j);

p(1,k)=x(i);

p(2,k)=y(j);

t(k)=z(i,j);

k=k+1;

end

end

figure(1), mesh(x,y,z);

net=newff(minmax(p),[3,1],{'tansig','purelin'},'trainlm');

net.trainParam.epochs=100;

%net.trainParam.goal=0.001;

net=train(net,p,t);

for i=1:n

for j=1:n

y(i,j)=sim(net,[x(i);y(j)]);

end

end

figure(2),mesh(x1,x2,y)

where file zad2.mat is generated here with this code:

clear all

n=25; k=50; h=1/n; N=n+1;

y = 0:h:1;

x=0:h:1;

for i = 1 : N

u(i,1)=0;

u(i,N)=x(i);

end

for j = 1 : N

u(1,j)=exp(y(j))+(1-exp(1))*(y(j)^2)-1;

u(N,j)=y(j);

end

for m=1:k

for i=2:n

for j=2:n

u(i,j)=(u(i-1,j)+u(i+1,j)+u(i,j-1)+u(i,j+1))/4;

end

end

end

figure(1), mesh(x,y,u)

figure(2), contour(u)

save zad2.mat x y u