MathGenie
diff
Differences and Approximate Derivatives
Syntax and Description
diff(X) 
calculates differences between adjacent elements of X along the first array dimension whose size does not equal 1:  If X is a vector of length m, then Y = diff(X) returns a vector of length m1. The elements of Y are the differences between adjacent elements of X. \[Y = \left[\begin{array}{cccc} X(2)X(1) & X(3)X(2) & ... & X(m)X(m1) \end{array}\right]\]
 If X is a nonvector pbym matrix, then Y = diff(X) returns a matrix of size (p1)bym, whose elements are the differences between the rows of X.
\[ Y = \left[ \begin{array}{c} X(2,:)X(1,:) \\ X(3,:)X(2,:) \\ \vdots \\ X(p,:)X(p1,:) \end{array}\right] \]

diff(X,n) 
calculates the nth difference by applying the diff(X) operator recursively n times. In practice, this means diff(X,2) is the same as diff(diff(X)). 
diff(X,n,dim) 
is the nth difference calculated along the dimension specified by dim. The dim input is a positive integer scalar. 
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