I have a nxn matrix(A) which has many zero rows and zero columns.. I removed the zero rows and columns using the command below such that Anew is now (n-m) x (n-m). After some computations on Anew matrix, I need to get Anew matrix back to nxn matrix.

I am removing the zero rows and zero columns from my matrix A using the command:

Anew=A(any(A,2),any(A,1)) ;where A(nxn) and Anew((n-m)x(n-m)) where there are m zero rows/columns

After some computation on Anew, I need to add the zero rows and columns back to their original position so that Anew now becomes nxn..

How to do it? Please help

Answer 1

[James Tursa]

temp = A;
temp(any(A,2),any(A,1)) = Anew;
Anew = temp;

[SanthoshKumar C]

This will copy my old matrix A to Anew. I need the new matrix(Anew) of size(n-m)x(n-m) to be nxn matrix by adding those zero rows and columns in appropriate position as removed previously..

[James Tursa]

Did you try my posted code? What is the size of the result? Are the zero rows & columns where they were originally in the A matrix?

[SanthoshKumar C]

Ur posted code will give Anew matrix of size nxn. But what I need is lil different.

Ex:

A=[1 0 2 0 3; 0 0 0 0 0; 4 0 5 0 6; 0 0 0 0 0; 7 0 8 0 9];

After the step,

Anew=A(any(A,2),any(A,1)) ;

Anew =

     1     2     3
     4     5     6
     7     8     9

Now I am doing some computation on Anew such that modified Anew will be as follows:

Anew = Anew+5

Anew =

     6     7     8
     9    10    11
    12    13    14

Last step: (Need to do this now) . Insert the zero rows and columns back to the original position in Anew such that Anew looks like this

Anew =

     6  0    7   0    8
     0  0    0   0    0
     9  0   10   0   11
     0  0    0   0    0
    12  0   13   0   14

[SanthoshKumar C]

Since I am working on matrix inverse of a (300+)x(300+) matrix which can have a more number of zero rows and columns (ill-conditioned matrix ofcourse).. Need robust way to do this

Answer 2

[SanthoshKumar C]

Thanks James Tursa.. I overlooked your answer.. Its working