Re: Octave Symbolic package: assign `nan` to symfun

[Colin Macdonald]

On 06/02/17 07:17, Nicholas Jankowski wrote:
> On Mon, Feb 6, 2017 at 8:59 AM, NVS Abhilash <address@hidden> wrote:
> > I am using the symbolic package, I have installed `2.5.0` from the source
> > [1]. I get this error in Octave 4.3.0+
>>
> > Is it a bug, or is it expected?
>
> Whether or not it's expected, this is 'compatible' behavior.  In Matlab 2016b:

I think its a least somewhat expected.  The same "problem" can be seen 
without the nan:

syms x
clear f     % (different behavior if f already exists)
f(x) = 7

The way to do this sort of thing is:

f(x) = sym(7)
f(x) = sym(nan)

I think there is not much we can do because Octave (and Matlab I expect) 
do not call address@hidden/subsasgn` in this case.  We could document it as a 
"gotcha" in "help symfun": pull request welcome.

Actually, perhaps address@hidden/subindex` could detect when its passed a Symbol 
and say something like:

  error ('are you perhaps trying to make a symfun from a non-sym rhs 
object?  If so, try using "f(x) = sym(<rhs>)"')

If you're not sure how to do these patches, you could file a bug at 
https://github.com/cbm755/octsympy/issues

cheers,
Colin