I have little knowledge about copulas and I dont know what should I do with data of stocks returns if I want to determine the relationship between returns. I know there are such copulas:
lowerBound(X, Y) = max(X + Y - 1, 0)
productCopula(X, Y) = X * Y
upperBound(X, Y) = min(X, Y)
How can I determine the relationship between returns using this?