Calculates the gradient function of a model with respect to a subset of the parameters given in
par_int, char_vars, evaluates it at the provided values and returns the result as
a function of the variable x.
gradient22(model, char_vars, values, par_int, weight_fun = function(x) 1)A function depending on x that's the gradient of the model with respect to char_vars
formula describing the model, which must contain only x, the parameters defined in
char_vars and the numerical operators.
character vector of the parameters of the model.
numeric vector with the nominal values of the parameters in char_vars.
vector of indexes indicating the subset of variables to omit in the calculation of the gradient.
optional one variable function that represents the square of the structure of variance, in case of heteroscedastic variance of the response