This function returns types of functions with shape constraints.
function.shape(shape = c("Free", "Increasing", "Decreasing",
"IncreasingConvex", "DecreasingConcave", "IncreasingConcave",
"DecreasingConvex", "IncreasingS", "DecreasingS",
"IncreasingRotatedS", "DecreasingRotatedS", "InvertedU", "Ushape"))
a vector giving types of shape restriction.