When Thursday Night Football is over, Big Bang and Life in Pieces will be followed by Mom and new comedy Angel From Hell and Elementary. Person of Interest, which did not get a full 22-episode order, will be held for midseason, as are 2 Broke Girls, Mike and Molly and The Odd Couple.
In statistics there are two kinds of means: population mean and sample mean. A population mean is the true mean of the entire population of the data set while a sample mean is the mean of a small sample of the population.
If only one variable has had values observed, then the sample mean is a single number (the arithmetic average of the observed values of that variable) and the sample covariance matrix is also simply a single value (a 1x1 matrix containing a single number, the sample variance of the observed values of that variable).