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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& l! \7 F1 f8 s$ m9 p& _net.trainParam.show = 50;
net.trainParam.lr = 0.05;
net.trainParam.epochs = 300;
net.trainParam.goal = 1e-5;
( j" v" ^* r* v! R: c' x6 Np = [-1 -1 2 2;0 5 0 5];
t = [-1 -1 1 1];
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  D+ f3 z2 ~$ A& Qnet=train(net,p,t);
/ ?- J* d/ X9 {, Q/ `; ZTRAINGD, 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
TRAINGD, Epoch 100/300, MSE 0.000435947/1e-05, Gradient 0.0161202/1e-10
TRAINGD, Epoch 150/300, MSE 8.68462e-05/1e-05, Gradient 0.00769588/1e-10
TRAINGD, Epoch 200/300, MSE 1.45042e-05/1e-05, Gradient 0.00325667/1e-10
" z+ E* a9 h2 E& p1 ZTRAINGD, Epoch 211/300, MSE 9.64816e-06/1e-05, Gradient 0.00266775/1e-10
TRAINGD, Performance goal met.
) q2 r  ~7 I% C7 y9 F0 }# \; na = sim(net,p)
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plot(p,t,p,a,'o')
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+ h  i: S# E- q% t! D. |3 n但是为什么老是报错：
! l: ]9 T0 y3 r& Y  w??? Input argument "net" is undefined.