MATLAB: Sparse to full matrix conversion not working…

fullissparseMATLABsparse

The functions full(.) and issparse(.) are behaving strangely for me. In particular, issparse(.) seems unable to detetct sparse matrices correctly, and full(.) fails to convert sparse matrices to full matrices. For example, when I run the code below:
S = sparse(double(rand(200,200) < 1/2));
SS = speye(200);
A = full(S);
AA = full(SS);
d1=issparse(S)
d2=issparse(SS)
d3=issparse(A)
d4=issparse(AA)
whos
I get the following output:
d1 =
     0
d2 =
     0
d3 =
     0
d4 =
     0
  Name        Size              Bytes  Class     Attributes
  A         200x200            321096  double    sparse    
  AA        200x200              4808  double    sparse    
  S         200x200            321096  double    sparse    
  SS        200x200              4808  double    sparse    
  ans         1x1                   8  double              
  d1          1x1                   8  double              
  d2          1x1                   8  double              
  d3          1x1                   8  double              
  d4          1x1                   8  double
So, issparse(.) tells me none of the matrices are sparse, while the "whos" command tells me that all four are sparse, when it should be the case that S and SS are sparse, while A and AA are not. Additionally, the Workspace window indicates that all four are sparse.
Any help with why this might be happening would be greatly appreciated. (The reason I need this is because a particular function I'm working with, schur(.), can only take full matrices as arguments.)

Best Answer

Something is definitely odd here. Your A and AA should be full matrices, not still sparse.
Let's make sure you're calling the correct issparse and full functions.
which -all issparse
which -all full
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