value

class value {
    public:
        value::value() { central = 1.0 ; error = 0.0 ; } 
        value::value(double a, double b) { central = a ; error = b ; } 
        
        double val() { return central ; } 
        double err() { return error ; } 

        value operator* (value v) {
            double error  =  (this->error * this->error * v.val() * v.val()) ;
            error +=  (v.err() * v.err() * this->value * this->value ) ;
            return value( this->central * v.val() , sqrt(error)) ;
            }   

        value operator/ (value v) {
            if (v.val() <= 0 ) return value(0.0,0.0) ;
            double error1  =  (this->error * this->error / v.val() / v.val()) ;
            double error2 +=  (v.err() * v.err() * this->value * this->value ) ;
            error2 /=  (v.val() * v.val() * v.val() * v.val() ) ;
            return value( this->central / v.val() , sqrt(error1+error2)) ;
            }  

    private:

        double central ;
        double error ;

};