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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net.trainParam.show = 50;
& n) g& f9 z2 P$ s9 unet.trainParam.lr = 0.05;
net.trainParam.epochs = 300;
net.trainParam.goal = 1e-5;
- P' k! [. _( t. T5 t8 Qp = [-1 -1 2 2;0 5 0 5];
3 ?- \1 `5 ]! U, }! Zt = [-1 -1 1 1];

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net=train(net,p,t);
TRAINGD, Epoch 0/300, MSE 1.59423/1e-05, Gradient 2.76799/1e-10

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TRAINGD, Epoch 50/300, MSE 0.00236382/1e-05, Gradient 0.0495292/1e-10
' }4 Z  ]+ i3 J. X# P/ ETRAINGD, Epoch 100/300, MSE 0.000435947/1e-05, Gradient 0.0161202/1e-10
. r8 R0 G6 R" Y/ P9 P0 N* iTRAINGD, Epoch 150/300, MSE 8.68462e-05/1e-05, Gradient 0.00769588/1e-10
4 \* G, S/ M9 b" c7 Y( _TRAINGD, Epoch 200/300, MSE 1.45042e-05/1e-05, Gradient 0.00325667/1e-10
2 D& Q7 b! _# RTRAINGD, Epoch 211/300, MSE 9.64816e-06/1e-05, Gradient 0.00266775/1e-10
  G+ m! j, ~' a& u- u7 s, I2 n; _TRAINGD, Performance goal met.
+ k# q& w% R8 i# R7 pa = sim(net,p)

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plot(p,t,p,a,'o')

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# j% p& t! D; {4 Y. Z& h7 z但是为什么老是报错：
??? Input argument "net" is undefined.