Artificial Neural Network Framework

First select the number of hidden layers, the number of neurons per layer and the function type (sigmoid or tanh).

Put your database into memory according to the main function example

Call the createNetworkStructure function, which will put the structure of the ANN into memory.

Train the network for a certain number of epochs using the trainNetwork function. You may also test the model at each epoch as depicted in the main function example.

For each prediction, call the forwardPass function

That's it!, you can now use a neural network !

A neural network with multi-layer perceptron is a graph structure where each node in an hidden layer is connected to every node in the following layer. But no connection exists between layers of a distance >= 2.

The network is trained using a backpropagation algorithm, here with the gradient descent. The concept is easy to understand : one forward pass is performed per object in the database. The output of the network is compared to what was expected, and the weights are updated to correct the output.

When should I use neural networks?

The use of ANN is recommended if :

• A lot of examples can be obtained easily
• The function you want to model is complex, but should exist
• Precision on output is not that important

If one of these conditions is not fulfulled, you should consider using another machine learning method, otherwise, go for ANNs !

#pragma argsused
int main(int argc, char* argv[])
{

int NbInput = 2;            //Number of input variables
int NbHidden = 2;           //Number of hidden layers
int NbNodes = 25;           //Number of nodes in each hidden layer
int NbOutput = 1;           //Number of output variables
int NbRuns = 500;           //Number of epochs
double LearningRate = 0.1;  //Learning rate (between 0 and 1)
int Type = 2;               //0 = sigmoide, 1 = identity (DON'T USE THIS), 2 = tanh

int DatabaseSize = 7;       //Number of objects in the database

NeuralNetwork nn;
double** TabOutput;
Elem* Database;
double* Outputs;
double* Inputs;

int i, j;


//Dynamic allocation
Database = (Elem*)malloc(DatabaseSize*sizeof(Elem));
for(i=0; i < DatabaseSize; i++)
{
    Database[i].Att = (double*)malloc(NbInput*sizeof(double));
    Database[i].GOAL = (double*)malloc(NbOutput*sizeof(double));
}

//Filling the database
Database[0].Att[0] = 0.1;
Database[0].Att[1] = 0.4;
Database[0].GOAL[0] = 0.25;
Database[1].Att[0] = 0.2;
Database[1].Att[1] = 1;
Database[1].GOAL[0] = 0.6;
Database[2].Att[0] = -0.3;
Database[2].Att[1] = 0.9;
Database[2].GOAL[0] = 0.3;
Database[3].Att[0] = 0.4;
Database[3].Att[1] = -0.4;
Database[3].GOAL[0] = 0.0;
Database[4].Att[0] = 0.9;
Database[4].Att[1] = 0.8;
Database[4].GOAL[0] = 0.85;
Database[5].Att[0] = 0.2;
Database[5].Att[1] = 0.7;
Database[5].GOAL[0] = 0.45;
Database[6].Att[0] = -0.1;
Database[6].Att[1] = 0.5;
Database[6].GOAL[0] = 0.2;

//Init the random seed
srand(time(NULL));

//Creating the network
nn = createNetworkStructure(NbInput, NbHidden, NbNodes, NbOutput, Type, LearningRate);

//Creating the array for output values
fprintf(stderr,"Creation of output array\n");
TabOutput = (double**)malloc((NbHidden)*sizeof(double*));
for(i = 0; i < NbHidden; i++)
{
    TabOutput[i] = (double*)malloc((NbNodes+1)*sizeof(double));
}

//Network training
for(i = 0; i < NbRuns; i++)
{
    trainNetwork(nn,TabOutput,1, Database, DatabaseSize);

    //Test
    Inputs = (double*)malloc((nn.NbInput+1)*sizeof(double));
    Inputs[0] = -0.3;
    Inputs[1] = 0.9;
    Inputs[2] = 1;
    Outputs = forwardPass(nn,TabOutput,Inputs);
    fprintf(stderr,"Average of 0.9 and -0.3 = %f (Expected : 0.3) \n",Outputs[0]);

    free(Outputs);
    Inputs[0] = 0.8;
    Inputs[1] = 0.9;
    Inputs[2] = 1;
    Outputs = forwardPass(nn,TabOutput,Inputs);
    fprintf(stderr,"Average of 0.8 and 0.9 = %f (Expected : 0.85) \n",Outputs[0]);

    free(Outputs);
    free(Inputs);

}
//Destruction of output array
fprintf(stderr,"Destruction of output array\n");
for(i = 0; i < NbHidden; i++)
    free(TabOutput[i]);
free(TabOutput);

//Destruction of the network
freeNetwork(nn);

//Destruction of the database
for(i = 0; i <  DatabaseSize; i++)
{
    free(Database[i].Att);
    free(Database[i].GOAL);
}
free(Database);

printf("Press  to quit...\n");
getchar();
return 0;
}