MATLAB: Deleting rows and columns of all zeroes in a symbolic matrix

deleting rows and columnssymbolic

Hello,

How can I delete all rows and columns of all zeroes in a symbolic matrix?

The solution listed here ( http://www.mathworks.com/matlabcentral/answers/40018-delete-zeros-rows-and-columns ) does not work when the matrix is symbolic. The any command produces an error "Unable to prove variable-name literally."

Thanks, Kevin

Best Answer

syms x1
data = [ x1, 1, 0 ; 0, 0, 0 ; 0, 1, 0]
data( all( isAlways(data==0) ,2) ,:) = []
data( : ,all( isAlways(data==0) ,1)) = []

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MATLAB: Deleting row and column with all zeros and putting it back

Another solution would be to never remove them in the first place

data=B{1,1}; data2=data;
r=any(data,2);
c=any(data,1);
data2(r,c)=inv(data(r,c));

MATLAB: How to delete specific columns from a matrix

Of course, it does not work:

for i = length(matrix):1

I assume you're trying to run the loop in reverse so that you don't shift rows yet to process as you delete rows. That's not how you tell matlab to run a loop in reverse. You have to specify the increment/decrement. Also, never use length on a matrix. If your n is less than 3, it'll return the number of columns instead and leads to interesting bugs. Always use size with an explicit dimension. So:

for i = size(matrix, 2):-1:1

would work. However, a loop is just a waste of time when it can all be accomplished in just one line with:

matrix(:, matrix(1, :) == 0) = [];

Best Answer

Related Solutions

MATLAB: Deleting row and column with all zeros and putting it back

MATLAB: How to delete specific columns from a matrix

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