MATLAB: Deactivation switch for implicit expansion

bsxfunimplicit expansionMATLAB

Does anyone know if there is a way to disable the implicit expansion feature introduced in R2016b?

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I believe it is not possible to disable the expansion. Personally, I like having it, just that people don't like change. There is some risk in implicit expansion, in that MATLAB novices will sometimes get hurt.

Now, could they introduce a settable flag, telling MATLAB to not use expansion? Yes, they surely could do so. The problem is then code written is no longer portable. Move your code to another computer that has the flag set off or on, and suddenly your code will not work. Or if your code sets the flag and someone uses your code, then suddenly you may have effectively introduced a bug into their code.

So, sorry but IMO, a flag or preference that can disable expansion is a bad idea.

Could you disable it yourself? I suppose you could overload the affected operators, checking for any case of implicit expansion. If you find it, then trap out with an error, saying that implicit expansion is just wrong in your humble opinion, and you won't allow it to work on your system. If no expansion is detected, then use the built-in operator. Yes, it will slow down your code. But it would work.

Related Solutions

MATLAB: How to avoid getting fooled by ‘implicit expansion’

 Should I just never trust any command to preserve the dimensions of my arrays,
 even if it's an inbuilt one?

The shapes of the output of built-in function have been subject to changes in the past and I expect this to happen in the future also. Therefore I catch my assumptions about shapes in a "unit-test" like function. So when I write

smoothed = smooth(EEG.data(iC,:), EEG.srate*60, 'moving');

I add this to the test function:

y = smooth(rand(1, 100), 5, 'moving');
if ~isrow
  error('SMOOTH does not reply a row vector for a row vector input.');
end

Nevertheless, it is a lot of work to do this for all assumptions. In many cases I'm not even aware of what I assume, e.g. for strncmp('hello', '', 2), which has changed its behavior in the past also.

In your case it would have been smart and efficient, if

deviation = EEG.data(iC,:) - smoothed

causes an error. Unfortunately the implicit expansion tries to handle this smartly, but it is smarter than the programmer in many cases. When it is intended, the implicit expansion is nice and handy, but it is an invitation for bugs also. All we can do is to live with it, because it is rather unlikely that TMW removes this feature. But I cannot be bad to write this as an enhancement request to them.

To answer the actual question:

 How do I avoid getting fooled by 'implicit expansion'?

Use Matlab < R2016b, at least for testing your code.

MATLAB: My code is in drop box. it works on the laptop but doesn’t work on PC

My guess (since we don’t have your code) is that your code uses ‘implicit expansion’ that was introduced in R2016b. You need to replace the ‘implicit expansion’ calculations that are throwing the error with bsxfun calls. That way, they will be compatible with prior MATLAB versions.

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Related Solutions

MATLAB: How to avoid getting fooled by ‘implicit expansion’

MATLAB: My code is in drop box. it works on the laptop but doesn’t work on PC

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