如何在MATLAB中给出层数组中的输入层?

我试图在Matlab中建立一个神经网络,它使用内置的 dropoutLayer

layers = [
    fullyConnectedLayer(hidden_layer_nodes(1))
    dropoutLayer(0.5)
    fullyConnectedLayer(hidden_layer_nodes(2))
    dropoutLayer(0.5)
    fullyConnectedLayer(hidden_layer_nodes(3))
    dropoutLayer(0.5)
    fullyConnectedLayer(output_layer_size)
    regressionLayer
    ];

我得到以下错误:

Error in main (line 54)
net = trainNetwork(X,y,layers,options);

Caused by:
    Network: Missing input layer. The network must have one input layer.
    Layer 1: Missing input. Each layer input must be connected to the output of another layer.

我理解这一点,因为我没有在layers数组中给出输入层。但我不确定我应该提供什么输入层,因为输入不是图像,也不是可用输入层的序列和列表:

1) 图像输入层

2) image3d输入层

4) 读出层 取自官方的Matlab文档。