Re: Ambiguous documentation for "clear -all"

[Michael D. Godfrey]

On 4/17/10 5:47 PM, Rik wrote:
> 4/17/10
>
> According to 'help clear', the option -all should clear local and global
> symbols.
>
> ---------------------------------------------------------------------
> The following options are available in both long and short form
>      `-all, -a'
>            Clears all local and global user-defined variables and all
>            functions from the symbol table.
> ---------------------------------------------------------------------
>
> However, Octave does not seem to actually remove the global variables, but
> only remove them from view.  The following code shows this:
>
> local_test_var = 1;
> global global_test_var = 2;
> whos
> clear -all
> whos
> global global_test_var
> global_test_var
>
> My question is whether we need to clarify the documentation to reflect what
> Octave actually does, or whether we should update Octave to do what the
> documentation says it does?  It would also be useful if someone could run
> the above code on Matlab ("clear -all" will need to be changed to "clear
> all" for Matlab).
>
> The documentation for Matlab's clear function is here:
> http://www.mathworks.com/access/helpdesk/help/techdoc/ref/clear.html.  The
> difference between "clear var" and "clear global var" is well explained.
>
> ---------------------------------------------------------------------
> If name is global, clear removes it from the current workspace, but it
> remains accessible to any functions declaring it global.
> ---------------------------------------------------------------------
>
> So it appears, that 'clear -all' is roughly equivalent to 'clear *',
> whereas I would have thought that 'clear -all' was equivalent to 'clear'
> which does remove both local and global variables.  Again, maybe someone
> can run the code above in Matlab and report what their parser thinks is
> correct.
>
> --Rik
>
>    
here is what matlab 2009b says.   Note that there are 2 changes 
required, which also
raise matlab compatibility questions.

First, matlab will not accept

global global_test_var = 2;


This has to be done in 2 steps.
No need to change Octave for this, I think!

Second, matlab does not accept -all.  It accepts -all and -a, but they 
do not
appear to do anything.  You have to say: clear all.
Octave appears to be similar:
octave:1>  xx=1;
octave:2> whos
Variables in the current scope:

  Attr Name        Size                     Bytes  Class
  ==== ====        ====                     =====  =====
       ans         1x13                       111  cell
       xx          1x1                          8  double

Total is 14 elements using 119 bytes

octave:3> global global_test =3;
octave:4> whos
Variables in the current scope:

  Attr Name             Size                     Bytes  Class
  ==== ====             ====                     =====  =====
       ans              1x13                       111  cell
    g  global_test      1x1                          8  double
       xx               1x1                          8  double

Total is 15 elements using 127 bytes

octave:5> clear all
octave:6> whos
octave:7> global_test
error: `global_test' undefined near line 7 column 1
octave:7>

After that here is what matlab says:
>> clear all
>> local_test_var = 1;
>> global global_test_var
>> global_test_var = 2;
>> whos
  Name                 Size            Bytes  Class     Attributes

  global_test_var      1x1                 8  double    global
  local_test_var       1x1                 8  double

>> clear all
>> whos
>>
>>
>> global global_test_var
>> global_test_var

global_test_var =

     []

>>
=======================================
It really removes all as does Octave without the -.
So it appears that the -all behavior is the main problem.
The current behavior of both matlab and Octave seems likely
to confuse.  Maybe a warning/error for clear -all  and clear -a  ?

Michael