Suppose x is an n-vector. the associated vector of differences is the (n−1)-vectordgivenbyd=(x2 −x1,x3 − −xn−1). expressdintermsofx using vector operations (e. g., slicing notation, sum, difference, linear combinations, inner product). the difference vector has a simple interpretation when x represents a time series. for example, if x gives the daily value of some quantity, d gives the day-to-day changes in the quantity.