Pairwise differences

I wish I'd known MATLAB had... DIFF

• DIFF calculates the sequential differences between numbers in an array. 
• It can work on any dimension along the array: Y = DIFF(X,2) calculates differences along the rows.
• For vectors, you can do a diff in different ways - e.g.
      Y = DIFF(X)   is similar to
      Y = [X nan]-[nan X] (except it has an 2 extra columns)
• Warning - DIFF(X) always has one fewer rows (or columns etc. depeding on dimension) than X! I often pad the diff with an extra row:
     Y = [ nan(1,size(X,2))
           DIFF(X)            ]

• Also note that there is a function GRADIENT that does something similar. In particular, the gradient at a point is calculated using the DIFF of the points on either side of it. So,
      Y=GRADIENT(X)        if X is a vector, is similar to
      Y=MEAN([ [nan;GRADIENT(X)], [GRADIENT(X),nan] ])
  except at the first and last points (thanks Sean Fallon for this info!).