Re: Bug when dividing a scalar by a vector?

[Sebastian Schöps]

> Am 12.01.2017 um 17:09 schrieb John W. Eaton <address@hidden>:
> 
> On 01/12/2017 10:42 AM, Sebastian Schöps wrote:
>> Montgomery-Smith, Stephen wrote
>>> My guess is that it is solving the underdetermined equation:
>>> 
>>> x1+x2+x3+x4=1.
>>> 
>>> So both solutions are correct answers.  There are infinitely many correct
>>> answers.
>>> 
>>> If I had to choose, I guess I would go for the answer who square sum is
>>> minimized, which would favor Octave's answer.
>> 
>> Thanks! That explains the behaviour and I agree that both solutions do make
>> sense. However, is that documented somewhere? Shouldn't there be a warning?
>> Similar to the case when a singular linear equation system is solved?
> 
> For which cases do you want warnings?
> 
> Do you want a warning because the particular solution is different from 
> Matlab,
no. This would be quite tedious :)

> or because the system is not square?
yes. My confusion popped up because 1./x was meant but 1/x was written in the 
code. Debugging took ages. Is this behaviour documented? - I use the Matlab 
language for more than 15 years and I was not aware!

> Does Matlab always warn when solving least-squares problems?

I checked: no, Matlab does not warn in the case of 1/x. It does warn if you 
solve a singular equation system ("Matrix is singular to working precision.") 
but it does not mention that a least squares solution will be returned. Older 
version of Octave were more explicit, right? I liked that but it seems that I 
missed that it was changed. 

Conclusion: there is no bug and no Matlab incompatibility. However, I think a 
warning would make sense even if Matlab does not. Sorry for the noise.
 
Bye
Sebastian