Learn more about MATLAB

Differencing Data

Three MATLAB functions perform finite difference calculations.

Function	Description
del2	Discrete Laplacian of a matrix
diff	Differences between successive elements of a vector; numerical partial derivatives of a vector
gradient	Numerical partial derivatives of a matrix

The diff function computes the difference between successive elements in a numeric vector. That is, diff(X) is [X(2)-X(1) X(3)-X(2)...X(n)-X(n-1)]. You might want to perform this operation on your data if you are more interested in analyzing the changes in the values, rather than the absolute values.

For a vector A,

A = [9 -2 3 0 1 5 4];
diff(A)

ans =
   -11     5    -3     1     4    -1

Besides computing the first difference, you can use diff to determine certain characteristics of vectors. For example, you can use diff to determine whether the vector values are monotonically increasing or decreasing, or whether a vector has equally spaced elements.

The following table provides examples for using diff with a vector x.

Test	Description
any(diff(x)==0)	Tests whether there are any repeated elements in X
all(diff(x)>0)	Tests whether the values are monotonically increasing
all(diff(diff(x))==0)	Tests for equally spaced vector elements

Detrending Data

Descriptive Statistics

© 1984-2009- The MathWorks, Inc.    -   Site Help   -   Patents   -   Trademarks   -   Privacy Policy   -   Preventing Piracy   -   RSS