matlab：神经网络中的零循环

Question

大家好！我想要循环的神经网络。我创建神经网络

net = newff(rand(5, 100), rand(1, 100), [3, 2], { 'tansig' 'tansig'}, 'traingdx3', 'learngdm', 'mse');
net.layerConnect(1, 1) = 1;
net.layerWeights{1, 1}.delays = [1];

net.trainParam.epochs = 100;

net = train(net, rand(5, 100), rand(1, 100));

和

net.LW

ans = 

    [3x3 double]              []    []
    [2x3 double]              []    []
              []    [1x2 double]    []

但是当我查看net.LW{1, 1}时，我得到了

net.LW{1, 1}

ans =

     0     0     0
     0     0     0
     0     0     0

为什么循环权重总是为零？