ActivationFunction.hpp

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#ifndef ACTIVATION_FUNCTION_HPP
#define ACTIVATION_FUNCTION_HPP
 
#include <base/Eigen.hpp>
#include <stdexcept>
 
namespace wbc{
 
enum activationType{NO_ACTIVATION,              
                    STEP_ACTIVATION,            
                    LINEAR_ACTIVATION,          
                    QUADRATIC_ACTIVATION,       
                    PROPORTIONAL_ACTIVATION};   
struct ActivationFunction{
    ActivationFunction() :
        type(NO_ACTIVATION){
    }
 
    double threshold;
    activationType type;
    base::VectorXd activation;
 
    const base::VectorXd &compute(const base::VectorXd& values){
 
        if(type != NO_ACTIVATION && (threshold < 0 || threshold > 1))
            throw std::invalid_argument("ActivationFunction::compute: Threshold must be within [0..1]");
 
        activation.resize(values.size());
        activation.setZero();
 
        for(uint i = 0; i < values.size(); i++){
            switch(type){
            case NO_ACTIVATION:
                activation(i) = 1;
                break;
            case STEP_ACTIVATION:
                if(fabs(values(i)) > threshold)
                    activation(i) = 1;
                else
                    activation(i) = 0;
                break;
            case LINEAR_ACTIVATION:
                if(values(i) < threshold)
                    activation(i) = (1.0/threshold) * values(i);
                else
                    activation(i) = 1;
                break;
            case QUADRATIC_ACTIVATION:
                if(values(i) < threshold)
                    activation(i) = (1.0/(threshold*threshold)) * (values(i)*values(i));
                else
                    activation(i) = 1;
                break;
            case PROPORTIONAL_ACTIVATION:
                if(values(i) < threshold)
                    activation(i) = values(i);
                else
                    activation(i) = 1;
 
                break;
            default:{
                std::stringstream s;
                s << "Invalid activation type: " << type;
                throw std::invalid_argument(s.str());
            }
            }
        }
        return activation;
    }
};
 
}
 
#endif