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：
" Y0 m7 }7 F7 A+ {- Z8 w: U: D5 znet=newff([-1 2; 0 5],[3,1],{'tansig','purelin'},'traingd');

# l& x' }# l9 D1 f. T) n
# c  f( w; o# L. z$ Z9 t3 J# r2 Wnet.trainParam.show = 50;
# L+ j6 f+ P& x# f) fnet.trainParam.lr = 0.05;
net.trainParam.epochs = 300;
net.trainParam.goal = 1e-5;
( R+ x. s. F4 E# ~9 z7 j$ \3 hp = [-1 -1 2 2;0 5 0 5];
3 s  m# Q8 E. b9 k$ ]; `1 }t = [-1 -1 1 1];

5 O6 b* B4 N: W3 E2 J
) V' O* x, h$ m9 }6 j; jnet=train(net,p,t);
* c- ?5 O: G- M' @' _# b1 I' U6 nTRAINGD, Epoch 0/300, MSE 1.59423/1e-05, Gradient 2.76799/1e-10
* y1 A, O+ F2 L( R

! N5 V" ?) G' W! ]. h6 r# W3 \; _3 bTRAINGD, Epoch 50/300, MSE 0.00236382/1e-05, Gradient 0.0495292/1e-10
2 t6 x7 ]$ G) S( a( i/ ?TRAINGD, Epoch 100/300, MSE 0.000435947/1e-05, Gradient 0.0161202/1e-10
2 ~/ J  B4 r- Y% 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
- }8 i! r6 ~9 H9 X) i4 o8 d" i3 J3 GTRAINGD, Epoch 211/300, MSE 9.64816e-06/1e-05, Gradient 0.00266775/1e-10
6 n5 q  N. X1 [TRAINGD, Performance goal met.
  z* c. H) Z0 T7 Q: S6 Aa = sim(net,p)
- M3 p3 w3 u) S1 \- ]" e

plot(p,t,p,a,'o')
6 ^8 ~2 \" ^6 M; G5 d! n6 k; `
, ?: H9 ^; [) }: _
但是为什么老是报错：
* |8 D5 `' `7 V, X??? Input argument "net" is undefined.