Gradient of the log-likelihood of a linear mixed model with random intercept
gradLMM(b, Y, X, ni)
a vector containing the gradient of the log-likelihood of the linear mixed model at point b
numeric vector specifying the parameter's values in the following order : first the fixed effects and then the standard deviation of the random intercept and of the independent error
numeric vector including the dependent outcome vector ordered by subject
numeric matrix including the covariates
interger vector giving the number of repeated measures for each subject