Hi, I would like to define a block matrix of size (n+m)x(n+m) as follows:
B11 B12
B21 B22
where B11 is (nxn) and B22 is (mxm). If I use the comma initializer as

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MatrixXd B(n+m,n+m);
B << B11, B12, B21, B22;


This works only if n and m are both non-zero. What can I do to support the possibility that either could be zero? I can use if statements to check, but that would quickly become unmanageable as the number of blocks increases.

Thanks!
S

I did not try, but I assume from your post that your code does not work if n or m are zero. I think that is a bug, so your best bet is to fix it and send a patch at http://eigen.tuxfamily.org/bz/ . If you cannot fix it yourself, a bug report at the same place would also be helpful in making sure we do not forget about it.

should be fixed:

https://bitbucket.org/eigen/eigen/chang ... 8f8406ee7/
changeset: 6d68f8406ee7
user: ggael
date: 2012-10-03 21:58:14
summary: fix comma initializer when inserting empty matrices
affected #: 1 file


https://bitbucket.org/eigen/eigen/chang ... d4ec16126/
changeset: 6fbd4ec16126
branch: 3.1
user: ggael
date: 2012-10-03 21:58:14
summary: fix comma initializer when inserting empty matrices
(transplanted from 6d68f8406ee739115a063d3524741411d5a23ab7)

This problem seems to have creeped in again.

If I run:

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  Eigen::VectorXd UL(3),U(3),L;
  UL<<U,L;

I get:

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Assertion failed: ((m_row+m_currentBlockRows) == m_xpr.rows() && m_col == m_xpr.cols() && "Too few coefficients passed to comma initializer (operator<<)"), function ~CommaInitializer, file /usr/local/include/eigen3/Eigen/src/Core/CommaInitializer.h, line 109.

( I have version 3.2.9 )

This has been fixed some weeks ago in both 3.2 and 3.3 branches.

On which minor/commit version of the 3.2 branch was this fixed again?

There is a bunch of commits that are all in 3.2.10:

10f2cc514f6c
1e7d97fea51d
75abaeb43845
44abf0a7b16a

but since the 3.2 branch does not fully handle empty matrices (irrespective to comma-init) there might be some unsupported cases (caught by assertions).