adapt (Neural Network Toolbox)

Neural Network Toolbox

adapt

Allow a neural network to adapt (change weights and biases on each presentation of an input)

Syntax

[net,Y,E,Pf,Af] = adapt(net,P,T,Pi,Ai)

To Get Help

Type help network/adapt

Description

This function calculates network outputs and errors after each presentation of an input.

[net,Y,E,Pf,Af,tr] = adapt(net,P,T,Pi,Ai) takes,

net -- Network

P -- Network inputs

T -- Network targets, default = zeros

Pi -- Initial input delay conditions, default = zeros

Ai -- Initial layer delay conditions, default = zeros

and returns the following after applying the adapt function net.adaptFcn with the adaption parameters net.adaptParam:

net -- Updated network

Y -- Network outputs

E -- Network errors

Pf -- Final input delay conditions

Af -- Final layer delay conditions

tr -- Training record (epoch and perf)

Note that T is optional and only needs to be used for networks that require targets. Pi and Pf are also optional and only need to be used for networks that have input or layer delays.

adapt's signal arguments can have two formats: cell array or matrix.

The cell array format is easiest to describe. It is most convenient for networks with multiple inputs and outputs, and allows sequences of inputs to be presented:

P -- Ni x TS cell array, each element P{i,ts} is an Ri x Q matrix

T -- Nt x TS cell array, each element T{i,ts} is a Vi x Q matrix

Pi -- Ni x ID cell array, each element Pi{i,k} is an Ri x Q matrix

Ai -- Nl x LD cell array, each element Ai{i,k} is an Si x Q matrix

Y -- NO x TS cell array, each element Y{i,ts} is a Ui x Q matrix

E -- Nt x TS cell array, each element E{i,ts} is a Vi x Q matrix

Pf -- Ni x ID cell array, each element Pf{i,k} is an Ri x Q matrix

Af -- Nl x LD cell array, each element Af{i,k} is an Si x Q matrix

where

Ni = net.numInputs

Nl = net.numLayers

No = net.numOutputs

Nt = net.numTargets

ID = net.numInputDelays

LD = net.numLayerDelays

TS = Number of time steps

Q = Batch size

Ri = net.inputs{i}.size

Si = net.layers{i}.size

Ui = net.outputs{i}.size

Vi = net.targets{i}.size

The columns of Pi, Pf, Ai, and Af are ordered from oldest delay condition to most recent:

Pi{i,k} = input i at time ts = k--ID

Pf{i,k} = input i at time ts = TS+k--ID

Ai{i,k} = layer output i at time ts = k--LD

Af{i,k} = layer output i at time ts = TS+k--LD

The matrix format can be used if only one time step is to be simulated (TS = 1). It is convenient for network's with only one input and output, but can be used with networks that have more.

Each matrix argument is found by storing the elements of the corresponding cell array argument in a single matrix:

P -- (sum of Ri) x Q matrix

T -- (sum of Vi) x Q matrix

Pi -- (sum of Ri) x (ID*Q) matrix

Ai -- (sum of Si) x (LD*Q) matrix

Y -- (sum of Ui) x Q matrix

Pf -- (sum of Ri) x (ID*Q) matrix

Af -- (sum of Si) x (LD*Q) matrix

Examples

Here two sequences of 12 steps (where T1 is known to depend on P1) are used to define the operation of a filter.

p1 = {-1  0 1 0 1 1 -1  0 -1 1 0 1};
t1 = {-1 -1 1 1 1 2  0 -1 -1 0 1 1};

Here newlin is used to create a layer with an input range of [-1 1]), one neuron, input delays of 0 and 1, and a learning rate of 0.5. The linear layer is then simulated.

```
net = newlin([-1 1],1,[0 1],0.5);
```

Here the network adapts for one pass through the sequence.

The network's mean squared error is displayed. (Since this is the first call of adapt, the default Pi is used.)

[net,y,e,pf] = adapt(net,p1,t1);
mse(e)

Note the errors are quite large. Here the network adapts to another 12 time steps (using the previous Pf as the new initial delay conditions.)

p2 = {1 -1 -1 1 1 -1  0 0 0 1 -1 -1};
t2 = {2  0 -2 0 2  0 -1 0 0 1  0 -1};
[net,y,e,pf] = adapt(net,p2,t2,pf);
mse(e)

Here the network adapts for 100 passes through the entire sequence.

p3 = [p1 p2];
t3 = [t1 t2];
net.adaptParam.passes = 100;
[net,y,e] = adapt(net,p3,t3);
mse(e)

The error after 100 passes through the sequence is very small. The network has adapted to the relationship between the input and target signals.

Algorithm

adapt calls the function indicated by net.adaptFcn, using the adaption parameter values indicated by net.adaptParam.

Given an input sequence with TS steps, the network is updated as follows. Each step in the sequence of inputs is presented to the network one at a time. The network's weight and bias values are updated after each step, before the next step in the sequence is presented. Thus the network is updated TS times.

See Also

sim, init, train, revert

Functions -- Alphabetical List boxdist