double IntegrationOfFunctions::calculate_trapezoid_integral(const Vector<double>& x, const Vector<double>& y)
{
int n = x.get_size();
double trapezoid_integral = 0;
for(int i = 0; i < n-1; i++)
{
trapezoid_integral += 0.5*(x[i+1]-x[i])*(y[i+1]+y[i]);
}
return(trapezoid_integral);
}