Same as function "mathWtsEfrontRisky" except that instead a user specified time series of portfolio asset returns, it is based on user specified returns mean vector and covariance matrix
mu.efront: A vector of specified efficient frontier mean returns
digits: Integer number of significant digits with default NULL
Returns
A matrix whose first row contains the mean returns along the efficient frontier, the second row contains the corresponding volatilities, and the remaining rows contain the components of the corresponding weight vectors.