新手求助~（关于初级的神经网络问题）

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各位大虾，我在网上看到的教程里的一个程序段，本来想要试试看的：
net=newff([-1 2; 0 5],[3,1],{'tansig','purelin'},'traingd');
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$ @; a/ L) J' A6 m# N- l8 snet.trainParam.show = 50;
net.trainParam.lr = 0.05;
net.trainParam.epochs = 300;
& k3 {- O2 v# ]- b- y0 m  i% Anet.trainParam.goal = 1e-5;
" {. L! G4 g; U, Ep = [-1 -1 2 2;0 5 0 5];
- D" I& i9 c, D# m% H* Jt = [-1 -1 1 1];

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net=train(net,p,t);
+ T! ~4 r  J. h9 l  L9 b. z' m- CTRAINGD, Epoch 0/300, MSE 1.59423/1e-05, Gradient 2.76799/1e-10
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& [' A3 B6 }. E6 D6 x' ?TRAINGD, Epoch 50/300, MSE 0.00236382/1e-05, Gradient 0.0495292/1e-10
TRAINGD, Epoch 100/300, MSE 0.000435947/1e-05, Gradient 0.0161202/1e-10
5 O" D( {( e# J6 o  k: a: z8 [TRAINGD, Epoch 150/300, MSE 8.68462e-05/1e-05, Gradient 0.00769588/1e-10
" K, ]* a9 N" k& I3 e  I5 H: i; X  ?TRAINGD, Epoch 200/300, MSE 1.45042e-05/1e-05, Gradient 0.00325667/1e-10
TRAINGD, Epoch 211/300, MSE 9.64816e-06/1e-05, Gradient 0.00266775/1e-10
TRAINGD, Performance goal met.
" c9 R  s; O7 m4 ~  La = sim(net,p)

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plot(p,t,p,a,'o')
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- k& A  O+ ~9 T但是为什么老是报错：
??? Input argument "net" is undefined.