新手求助~（关于初级的神经网络问题）

Continue

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：
2 J" q+ K/ m) `" z' r9 nnet=newff([-1 2; 0 5],[3,1],{'tansig','purelin'},'traingd');
" O6 N+ T/ c- @9 w/ W0 |$ V

net.trainParam.show = 50;
net.trainParam.lr = 0.05;
net.trainParam.epochs = 300;
' T( H4 S4 l% Unet.trainParam.goal = 1e-5;
) n2 |2 j! d3 H3 f: e3 R7 {p = [-1 -1 2 2;0 5 0 5];
t = [-1 -1 1 1];
& G$ F5 ^- F# [! s) B9 h
5 n/ i% }, S. x6 g
1 v2 n; |  B( B! {4 |4 C0 Inet=train(net,p,t);
/ {- `, h9 l$ O8 STRAINGD, Epoch 0/300, MSE 1.59423/1e-05, Gradient 2.76799/1e-10
9 k" r4 O8 e" |# U, e, p4 o- F( @

& v" X8 M9 q# K3 h1 CTRAINGD, Epoch 50/300, MSE 0.00236382/1e-05, Gradient 0.0495292/1e-10
. e' h" _& _1 \" [9 Y! m( bTRAINGD, 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
# B: A0 o; I) l3 m. z0 J( l$ K& u- q1 JTRAINGD, Epoch 211/300, MSE 9.64816e-06/1e-05, Gradient 0.00266775/1e-10
* @4 Q- y% f" YTRAINGD, Performance goal met.
/ k5 z5 Q  E- s/ A% v: Da = sim(net,p)

, v' E% R6 o8 A% ]
* L7 _  ]% D! @5 R8 L. v' c2 {; p& Uplot(p,t,p,a,'o')

5 P3 b2 y2 J, U8 t4 l: p8 x
但是为什么老是报错：
/ s$ G/ s% B( |( j* G/ m??? Input argument "net" is undefined.