Y = wmean(X,RANGE,BETA)
X [ tseries ] - Input tseries object whose data will be averaged column by column.
RANGE [ numeric ] - Date range on which the weighted average will be computed.
BETA [ numeric ] - Discount factor; the last observation gets a weight of of 1, the N-minus-1st observation gets a weight of BETA, the N-minus-2nd gets a weight of BETA^2, and so on.
Y [ numeric ] - Array with weighted average of individual columns; the sizes of Y are identical to those of the input tseries object in 2nd and higher dimensions.