Return or set gradient attribute
gradient(x, ...)# S3 method for default
gradient(x, ...)
gradient(x, ...) <- value
# S3 method for default
gradient(x, ...) <- value
any R object
additional paramters
new gradient value to set
attr(x,"gradient")
gradient attribute is used by loss/risk function to return the gradient of the function at a given point together with the function value