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：
8 A# f% e8 F4 ~7 n7 S+ b) W7 Pnet=newff([-1 2; 0 5],[3,1],{'tansig','purelin'},'traingd');

: L6 V+ P( j, U4 Q
net.trainParam.show = 50;
( [: }" ~# [7 onet.trainParam.lr = 0.05;
net.trainParam.epochs = 300;
* s# }6 z4 y8 z; Unet.trainParam.goal = 1e-5;
: Z7 b  K& k4 @# n8 ~" g0 yp = [-1 -1 2 2;0 5 0 5];
t = [-1 -1 1 1];

& d# p+ h0 Z0 P0 s/ F  n# v6 c
  {* O, f4 T$ p+ f# U. o. ]. t) Enet=train(net,p,t);
2 m8 I. [0 H/ TTRAINGD, Epoch 0/300, MSE 1.59423/1e-05, Gradient 2.76799/1e-10

: D2 H9 v! Q" _& r, J$ H
TRAINGD, Epoch 50/300, MSE 0.00236382/1e-05, Gradient 0.0495292/1e-10
! u/ l" B& f# {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
9 r1 ]1 w3 k& B( N! a0 ]' X: ^TRAINGD, Epoch 211/300, MSE 9.64816e-06/1e-05, Gradient 0.00266775/1e-10
TRAINGD, Performance goal met.
a = sim(net,p)


& B2 m  o9 e2 W1 wplot(p,t,p,a,'o')


但是为什么老是报错：
" ?+ k9 ~* ?3 u# A. c- |??? Input argument "net" is undefined.