2.66 How to add the mean of each row of a matrix from each row?

Given

\[ \left ( {\begin {array} {cc} 1 & 2 \\ 3 & 4 \end {array}} \right ) \]

Find the mean of each row, and add this mean to each element of the corresponding row. The result should be

\[ \left ( {\begin {array} {cc} 2.5 & 3.5 \\ 6.5 & 7.5 \end {array}} \right ) \]

To subtract the mean, just replace Plus with Subtract below for Mathematica and replace @plus with @minus for Matlab. This shows that Matlab bsxfun is analogue to Mathematica’s MapThread.. The main difference is that Matlab is a little bit more consistent in this example, since in Matlab all operations are done column wise. Hence mean(A) takes the mean of each column (same as Matematica in this one case), but bsxfun also acts column wise on the matrix A, while Mathematica Map and MapThread act row wise (list of lists). One just needs to be careful about this order difference.

Mathematica mat = {{1, 2}, {3, 4}}; MapThread[Plus,{mat, Mean@Transpose@mat}] // N

{{2.5, 3.5}, {6.5, 7.5}}

 

Matlab A=[1 2;3 4]; bsxfun(@plus, A', mean(A'))

ans = 2.5 6.5 3.5 7.5

 

Maple A:=Matrix([[1,2],[3,4]]); for n from 1 to LinearAlgebra:-RowDimension(A) do A[n,..]:=A[n,..] +~ Statistics:-Mean(A[n,..]) od; A

\[ \left [\begin {array}{cc} 2.5000000000 & 3.5000000000 \\ 6.5000000000 & 7.5000000000 \end {array}\right ] \]