Bivariate function data objects are functions of two arguments, $f(s,t)$. It can be useful to evaluate the function for argument values satisfying $s=t$, such as evaluating the univariate variance function given the bivariate function that defines the variance-covariance function or surface. A linear differential operator can be applied to function $f(s,t)$ considered as a univariate function of either object holding the other object fixed.
evaldiag.bifd(evalarg, bifdobj, sLfd=int2Lfd(0), tLfd=int2Lfd(0))a vector of values of $s = t$.
a bivariate functional data object of the bifd class.
either a nonnegative integer or a linear differential operator object.
either a nonnegative integer or a linear differential operator object.
a vector or matrix of diagonal function values.