sigmoid_d.cpp

vector <float> sigmoid_d (const vector <float>& m1) {
    
    /*  Returns the value of the sigmoid function derivative f'(x) = f(x)(1 - f(x)), 
        where f(x) is sigmoid function.
        Input: m1, a vector.
        Output: x(1 - x) for every element of the input matrix m1.
    */
    
    const unsigned long VECTOR_SIZE = m1.size();
    vector <float> output (VECTOR_SIZE);
    
    
    for( unsigned i = 0; i != VECTOR_SIZE; ++i ) {
        output[ i ] = m1[ i ] * (1 - m1[ i ]);
    }
    
    return output;
}