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：
net=newff([-1 2; 0 5],[3,1],{'tansig','purelin'},'traingd');

2 s; o& d0 l7 j* d3 N- ~
net.trainParam.show = 50;
1 n, d5 T2 G' [1 w2 P+ Ynet.trainParam.lr = 0.05;
net.trainParam.epochs = 300;
net.trainParam.goal = 1e-5;
+ g. e1 x# L# {& p. f6 |  n' Kp = [-1 -1 2 2;0 5 0 5];
t = [-1 -1 1 1];
3 p  X4 Y5 Z( l7 Y( H' h
8 Z0 a7 _- S; y9 T  f# x
net=train(net,p,t);
TRAINGD, Epoch 0/300, MSE 1.59423/1e-05, Gradient 2.76799/1e-10


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
) T0 P; Q  b8 K7 y. TTRAINGD, Epoch 200/300, MSE 1.45042e-05/1e-05, Gradient 0.00325667/1e-10
  ?, F1 P+ I8 ]  D1 CTRAINGD, Epoch 211/300, MSE 9.64816e-06/1e-05, Gradient 0.00266775/1e-10
TRAINGD, Performance goal met.
a = sim(net,p)


plot(p,t,p,a,'o')


但是为什么老是报错：
??? Input argument "net" is undefined.