A vector-valued function y of a real variable sends real numbers to vectors in some vector space R"n". A vector-valued function can be split up into its coordinate functions , meaning that . This includes, for example, parametric curves in R2 or R3. The coordinate functions are real valued functions, so the above definition of derivative applies to them. The derivative of y("t") is defined to be the vector, called the tangent vector, whose coordinates are the derivatives of the coordinate functions. That is,