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：
3 h$ Q/ |  J! s3 {% `. Rnet=newff([-1 2; 0 5],[3,1],{'tansig','purelin'},'traingd');
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# `8 S% D: r. }$ q# [& x+ Rnet.trainParam.show = 50;
net.trainParam.lr = 0.05;
net.trainParam.epochs = 300;
; ^0 ?9 A; ~& [" E! Knet.trainParam.goal = 1e-5;
p = [-1 -1 2 2;0 5 0 5];
t = [-1 -1 1 1];
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! J# Z# F  w* \net=train(net,p,t);
' a. D" s# x6 p* e  FTRAINGD, Epoch 0/300, MSE 1.59423/1e-05, Gradient 2.76799/1e-10

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9 o) g9 o+ `/ Z0 t& R2 ?6 KTRAINGD, Epoch 50/300, MSE 0.00236382/1e-05, Gradient 0.0495292/1e-10
9 o5 w/ u( X( `! @TRAINGD, Epoch 100/300, MSE 0.000435947/1e-05, Gradient 0.0161202/1e-10
. A7 {& \' e7 ~$ pTRAINGD, 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
( c; S3 K8 h6 @6 Y- j- _% [9 Z6 R, c! z; xTRAINGD, Epoch 211/300, MSE 9.64816e-06/1e-05, Gradient 0.00266775/1e-10
TRAINGD, Performance goal met.
a = sim(net,p)
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/ l) X9 y, A8 Q2 y% D" ~plot(p,t,p,a,'o')

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' U1 m2 W8 d0 m, C1 O2 q但是为什么老是报错：
??? Input argument "net" is undefined.