Re: matlab nargin() function alternative in octave?

[taltman]

Hi Sharene,

Whether you do checks from the call-side, or you do checks from the
called-function-side, you still must do a check.

To avoid using global variables, I'd advocate for a (message-)dispatch
approach:

1. have your main function that you want to test ("myfunc")

2. "myfunc" will receive a variable number of arguments.

3. based on the inputs, you dispatch the data to the correct version
   of your real function ("myfunc1", "myfunc2")

I'd advocate this usage over modifying all the calls to this
function. You won't need global variables, and you just need to modify
one function. Plus, it's always good coding practice to check a
function's inputs. Since you're checking the inputs anyways, why not
put in some extra logic to take care of the two cases?

Just my $0.02,

~Tomer



On Jan 20, 2004 at 6:14pm, Sharene Deanne Bungay wrote:

sbunga >Date: Tue, 20 Jan 2004 18:14:11 -0500
sbunga >From: Sharene Deanne Bungay <address@hidden>
sbunga >To: address@hidden
sbunga >Cc: address@hidden
sbunga >Subject: Re: matlab nargin() function alternative in octave?
sbunga >Resent-Date: Tue, 20 Jan 2004 17:17:02 -0600
sbunga >Resent-From: address@hidden
sbunga >
sbunga >Hi Tomer,
sbunga >Thank you for your suggestion. Unfortunately, using variable arguments
sbunga >will not solve my particular problem without significant rewrites of
sbunga >existing code. I may be able to shed more light on the subject with
sbunga >another example:
sbunga >Let's say for example that I have a large algorithm that calls a
sbunga >function as one of its steps. Now, let's say that I wish to try out
sbunga >two completely different implementations of this function, but that
sbunga >the two different implementations require different arguments, or even
sbunga >to have different global variables set to specific values. I don't want
sbunga >to make extensive changes to my algorithm, so instead, I just wish
sbunga >to test the number of arguments my function needs to take, and based on
sbunga >this, set up the required global variables. Something like,
sbunga >if (nargin('myfunc')==3)
sbunga >   myglobal=3.45;
sbunga >endif
sbunga >I.e. I only would want to change myglobal to be 3.45 *IF* myfunc takes 3
sbunga >arguments. So the issue is not how to handle a different number of
sbunga >arguments _within_ a function, but rather to tell how many arguments
sbunga >a function _expects_ to take, while outside the scope of that function.
sbunga >For a given run, the function itself is defined to take only say, 2 or
sbunga >3 arguments (exclusive or). A quick hack would be to declare a global
sbunga >that merely stores a flag indicating what way our function is defined
sbunga >(say myflag=2 or myflag=3 for myfunc() defined for 2 or 3 arguments
sbunga >respectively) and then to change all of the nargin('myfunc')==3 checks
sbunga >to if (myflag==3). However, this doesn't answer my question as to if
sbunga >there is a way in octave to get the number of arguments expected by a
sbunga >defined function, outside the scope of that function.
sbunga >
sbunga >I hope this helps explain the issue a bit better.
sbunga >All ideas are appreciated!
sbunga >Cheers,
sbunga >Sharene
sbunga >
sbunga >On Tue, 2004-01-20 at 17:06, address@hidden wrote:
sbunga >> This looks like it can be handled using 'varargin'. It can allow your
sbunga >> function to accept a variable number of arguments. You'll just have to
sbunga >> do some variable type-checking.
sbunga >> 
sbunga >> HTH,
sbunga >> 
sbunga >> ~Tomer
sbunga >> 
sbunga >> 
sbunga >> 
sbunga >> On Jan 20, 2004 at 10:04am, Sharene Bungay wrote:
sbunga >> 
sbunga >> sbunga >Date: Tue, 20 Jan 2004 10:04:44 -0500 (EST)
sbunga >> sbunga >From: Sharene Bungay <address@hidden>
sbunga >> sbunga >To: John W. Eaton <address@hidden>
sbunga >> sbunga >Cc: address@hidden
sbunga >> sbunga >Subject: Re: matlab nargin() function alternative in octave?
sbunga >> sbunga >Resent-Date: Tue, 20 Jan 2004 09:04:48 -0600
sbunga >> sbunga >Resent-From: address@hidden
sbunga >> sbunga >
sbunga >> sbunga >Hi, thanks for your reply.
sbunga >> sbunga >I believe it can only accept string arguments under matlab.
sbunga >> sbunga >An example is as follows: Lets assume that I define
sbunga >> sbunga >an algorithm that uses regression as one of its steps.
sbunga >> sbunga >I code the algorithm to call reg(x1,x2,...) with the
sbunga >> sbunga >correct number of arguments. reg() in turn is conditionally
sbunga >> sbunga >defined to take either say, 2 or 3 arguments, depending
sbunga >> sbunga >on some user-set parameter. I could then have my algorithm
sbunga >> sbunga >test something like:
sbunga >> sbunga >
sbunga >> sbunga >if (nargin('reg')==3)
sbunga >> sbunga >      sigma=0.001;
sbunga >> sbunga >      reg(x1,x2,sigma);
sbunga >> sbunga >else
sbunga >> sbunga >      reg(x1,x2);
sbunga >> sbunga >end
sbunga >> sbunga >
sbunga >> sbunga >Now if I were coding this, I would probably just have a global
sbunga >> sbunga >flag something like:
sbunga >> sbunga >
sbunga >> sbunga >if (userselect==reg1)
sbunga >> sbunga >      regfunc1(x1,x2,sigma);
sbunga >> sbunga >else
sbunga >> sbunga >      regfunc2(x1,x2);
sbunga >> sbunga >end
sbunga >> sbunga >
sbunga >> sbunga >But unfortunately, I need to use existing code that makes
sbunga >> sbunga >use of the nargin('string') functionality.
sbunga >> sbunga >
sbunga >> sbunga >TIA.
sbunga >> sbunga >Sharene.
sbunga >> sbunga >
sbunga >> sbunga >On Mon, 19 Jan 2004, John W. Eaton wrote:
sbunga >> sbunga >
sbunga >> sbunga >> On 19-Jan-2004, Sharene Deanne Bungay <address@hidden> 
wrote:
sbunga >> sbunga >> 
sbunga >> sbunga >> | I have some matlab code that I would very much like
sbunga >> sbunga >> | to use under octave. Unfortunately, the matlab code
sbunga >> sbunga >> | relies on matlab's ability to pass a function as an
sbunga >> sbunga >> | argument to nargin ( eg. nargin('sin')) and have it return
sbunga >> sbunga >> | the number of arguments expected by that function.
sbunga >> sbunga >> | I know that under octave, nargin is only a local scope 
scalar
sbunga >> sbunga >> | valid inside a given function, but does there exist a 
means
sbunga >> sbunga >> | under octave to get the number of expected arguments to a 
function
sbunga >> sbunga >> | (outside the scope of that function)?
sbunga >> sbunga >> | 
sbunga >> sbunga >> | (This functionality is required since I have functions 
that are
sbunga >> sbunga >> | conditionally defined to take different arguments, and 
subsequent
sbunga >> sbunga >> | behaviour requires knowledge of the number of arguments. 
Rewriting
sbunga >> sbunga >> | the code to use global variables instead of relying on 
the form of
sbunga >> sbunga >> | the function definitions would be too extensive, so any 
help
sbunga >> sbunga >> | on this matter would be *GREATLY* appreciated.)
sbunga >> sbunga >> 
sbunga >> sbunga >> Can you post an actual example that uses this functionality 
so we can
sbunga >> sbunga >> see how you are using it and why it is needed?
sbunga >> sbunga >> 
sbunga >> sbunga >> The Matlab documentation shows that nargin and nargout may 
accept
sbunga >> sbunga >> string arguments.  Are function handles also allowed?
sbunga >> sbunga >> 
sbunga >> sbunga >> Thanks,
sbunga >> sbunga >> 
sbunga >> sbunga >> jwe
sbunga >> sbunga >> 
sbunga >> sbunga >
sbunga >> sbunga >
sbunga >> sbunga >
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