[Octave-bug-tracker] [bug #60784] Inconsistent behavior for boolean matrix types with matrix functions

[Kai Torben Ohlhus]

Update of bug #60784 (project octave):

                Severity:              3 - Normal => 1 - Wish               
                Priority:              5 - Normal => 1 - Later              
                  Status:                    None => Need Info              

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Follow-up Comment #1:

Thanks for the report.  I agree, that inconsistency can be annoying.  In this
case I tend to support the current Matlab R2021a implementation


>> A = logical (rand (4));
>> det (A)
Check for incorrect argument data type or missing argument in call to function
'det'.
 
>> eig (A)
Error using eig
Invalid data type. Input matrix must be double or single.


(same for inv(A), svd(A), and lu(A)) to strictly forbid calling those function
with non-single or non-double input.

It is more for user convenience, but making a type cast explicit helps in
understanding memory issues and avoids ugly surprises.  For example


>> A = rand (2e4);   ##   3 GB
>> B = logical (A);  ## 380 MB

>> tic; det (A), toc
ans = -Inf
Elapsed time is 223.995 seconds.
>> tic; det (B), toc
ans = 0
Elapsed time is 136.939 seconds.
tic; det (double (B)), toc
ans = 0
Elapsed time is 135.042 seconds.


An unaware programmer might think if "det (B)" is permitted, there must be a
memory efficient implementation for "logical" matrices in Octave.

However, running the example and observing a memory monitor shows a slightly
bigger memory blowup (as the original 380 MB matrix B has to be stored on top
of the internal conversion to a full double matrix).  Thus one gets an even
worse memory usage, even though I did everything to save memory using a
logical array 😓

In my opinion, the discussion boils down to convenience vs. no surprises.  As
said before, I prefer no surprises.

How do other maintainer think about it? 🙂  Is it worth ensuring consistency
and if yes, convenience or no surprises (Matlab compatibility)?


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