[Octave-bug-tracker] [bug #35157] Naive users baffled by "complex scalar type invalid as index value"

[Michael Godfrey]

Follow-up Comment #5, bug #35157 (project octave):

There will always be people who do not read or
understand error messages.  But, the messages should be 
made clearer, simpler, and more precise whenever possible.

In this case I agree that the error message was not clear,
and the suggested improvement was not much better.

Many users are not clear about what variables are predefined.

A simple improvement in this case would be to use the message
that you get for:

octave:1> a(1.23)=1
error: subscript indices must be either positive integers or logicals
octave:1>

instead of:
octave:1> a(j)=1
error: complex scalar type invalid as index value
error: assignment failed, or no method for `<unknown type> = scalar'
octave:1> 

Note this case:
octave:1> a(e)=1
error: subscript indices must be either positive integers or logicals
octave:1> 

It does not make sense to treat "e" differently from "i" or
"j".

Somewhat related to this, I tried to lookup what variables
are predefined in Octave.  I could not find a Section in
the Manual that lists these, nor did searches of the pdf
find anything.  Ideally, such a Section should be generated
from the current Octave code.  And, a command ("predefined" ?)
would be useful.

Does anyone know where to start in the source files to find
them all?



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