Class ModelParameter represents a parameters theta
included in f(x,theta)
theta = mu, covariance_matrix
mu - parameter that acts in the individual model
covariance_matrix - additional parameter for the population model
theta_distribution - Distribution.
Objects form the class ModelParameter can be created by calls of the form ModelParameter(...) where
(...) are the parameters for the ModelParameter objects.
name:A character string giving the name of the parameter.
mu:A numeric giving the value of the mean mu.
omega:A numeric giving the value of the variance.
distribution:An object of the class Distribution.
fixed:A boolean giving if the parameter is fixed or remain to be estimated.
fixedMu:A boolean giving if the mean mu is fixed or remain to be estimaed.