Neural Network Code NullPointerException help

penumbra · 05-11-2012, 09:53 PM

This is a long but basic question, no knowledge on neural networks is required. Posted a pic of me to offer an incentive.

So I'm currently working on implementing a neural network. It should all work...but obviously it doesn't. The project has 3 classes
-NeuralNetwork which is "where all the magic happens"
-NeuralLayer which just keeps track of the nodes in a layer
-NeuralNode which keeps track of a node's value, weights it's sending out, and bias (none of that is really important)

just thought I'd point out that there are other classes.

In the main I have among other things:

Code:

net.runAll(15);

where 15 represents the number of times to run the network.

Here's the runAll method

Code:

public void runAll(int numTimes) //number of iterations for running the network
    {
        initializeRandomWeights();
        int count=0;
        trainingRate = .1;

        while (count < numTimes)
        {
            forward();
            calcOutputDelta();
            for (int L=layers.length-1; L>0; L--)
            {
                updateWeights(L-1);
                updateBias(L);
                calcLayerDelta(L-1);
            }
            count++;
            trainingRate *= .9999;
        }
    }

the important thing to note is the initializeRandomWeights in the first line of the method which calls these two methods.

Code:

    public void initializeRandomWeights() //set random weights and bias
    {
        NeuralLayer nextLayer; //layer of nodes recieving the weights
        double[] rWeights; //random weights
        double rBias;
        for (int L=0; L<layers.length-1; L++)
        {
            for (int n=0; n<layers[L].getSize(); n++)
            {              //I initially had this statement after "nextLayer = layers[l+1];" but I realized it
                rWeights = randomWeights(L);         //has to be in this loop 
                rBias = Math.random()*2;       //or else it would send the same array to all the nodes
                layers[L].getNodeAt(n).setBias(rBias);
                layers[L].getNodeAt(n).setWeights(rWeights);    
            }
        }
    }

    public double[] randomWeights(int layer)
    {
        int size = layers[layer+1].getSize();        
        double[] w = new double[size];
        for (int i=0; i<size; i++)
            w[i] = Math.random()*2;
        return w;
    }

and this should go through each layer excluding the last/output and put in random weights for all the nodes in those layers (weights are being sent out by nodes so the last/output layer wouldnt send any)

also in the runAll method I have a call to the method forward which just calculates the values for all the nodes based on their weights going forward. Here's that code:

Code:

    public void forward()
    {
        NeuralNode node;
        for(int L=1; L<layers.length; L++)
        {
            for (int n=0; n<layers[L].getSize(); n++)
            {
                node = new NeuralNode(calcNode(L, n));
                layers[L].setNodeAt(n, node);
            }
        }
    }

and the calcNode method is:

Code:

public double calcNode(int layer, int node)
    {
        double sum = 0.0;
        for (int i=0; i<layers[layer-1].getSize(); i++)
        {
            sum += layers[layer-1].getNodeAt(i).getValue()*getWeightFrom(layer-1, i, node);
        }
        sum += layers[layer].getNodeAt(node).getBias();
        return sigmoid(sum);
    }

when I run the main, I get a NullPointerException

Code:

java.lang.NullPointerException
	at NeuralNode.getWeightTo(NeuralNode.java:25)
	at NeuralNetwork.getWeightFrom(NeuralNetwork.java:79)
	at NeuralNetwork.calcNode(NeuralNetwork.java:97)
	at NeuralNetwork.forward(NeuralNetwork.java:110)
	at NeuralNetwork.runAll(NeuralNetwork.java:180)
	at NeuralNetwork.main(NeuralNetwork.java:206)

and I'm assuming it means one of the weights it's trying to reference has not been initialized, but initializeRandomWeights should initialize them all. Is there any way that initializeRandomWeights is not getting called?

I realize this is a lengthy question, and I thank anyone who has taken the time to read it.

neural_nut · 05-12-2012, 12:22 PM

Hey!

Firstly, apologies if my response is off the mark, I havent been coding in over ten years, your mail hit my radar becauseit contained the words neural and code.

Two tips:

1) the variables being initialised in the functin initialiseall wont exist outside of that function. You either need to make the variables public static variables in the class or pass the initialisation results back out to the calling function and apply them to variables there.

2) giving the photo incentive with the question doesnt incentivise giving a response! Should be photo for answer :-)

Hope thathelps

NN

PS. Sent from my eeePad so please excuse punctuation mistakes.