Re: Chebfun

[Jaroslav Hajek]

On Sat, Jan 23, 2010 at 6:50 AM, Michael D Godfrey
<address@hidden> wrote:
> On 01/22/2010 09:37 PM, Jaroslav Hajek wrote:
>
> On Fri, Jan 22, 2010 at 4:52 PM, Daniel Pfenniger
> <address@hidden> wrote:
>
>
>> Hello,
>>
>> Chebfun (http://www2.maths.ox.ac.uk/chebfun/) adds very powerful
>> capabilities
>> to Matlab, making numerical computations feeling like symbolic ones, with
>> the
>> speed of numerical computations.
>> It would be nice if Octave could profit from this major advance.
>>
>> However Chebfun v 3.0 is not working in Octave due to some missing
>> capability
>> in Octave.
>>
>> I am not at all familiar with the internals of Matlab or Octave, but
>> perhaps
>> someone on this list can evaluate if the problem is hard or easy to solve.
>
>
> Indeed few people are familiar with Matlab internals, given they're secret
> :)
>
>
>
>> Making Chebfun working could also suggest where efforts for Octave should
>> go.
>>
>> When I try to define a chebfun on Octave 3.2.4 I get the following :
>>
>> ----------------------------
>> octave:22> x = chebfun('x',[0 10]);
>> error: concatenation operator not implemented for `scalar' by `class'
>> operations
>> error: called from:
>> error:   /home/pf/Trefethen/chebfun/@chebfun/private/ctor_adapt.m at line
>> 119, column 6
>> error:   /home/pf/Trefethen/chebfun/@chebfun/chebfun.m at line 153, column
>> 7
>> octave:22>
>> -----------------------------
>>
>> In the file ctor_adapt.m  funs is initialized as
>>
>> funs = [];
>>
>> and later updated as
>>
>> funs = [funs fs];
>>
>> which produces the error message. fs results from a call to a the function
>> fun with the following header:
>>
>> -------------------------------------------------------
>> function [g,ish] = fun(op,ends,varargin)
>> % FUN   Constructor
>> % FUN(OP,ENDS) constructs a fun object for the function OP.  If OP is a
>> string,
>> % such as '3*x.^2+1', or a function handle, FUN(OP) automatically
>> determines
>> % the number of points for OP. If OP is a vector, FUN(OP) constructs a fun
>> % object such that its function values are the numbers in OP.
>> %
>> % FUN(OP,ENDS,N) where N a positive integer creates a fun for OP with N
>> Chebyshev
>> % points. This option is not adaptive.
>> %
>> % FUN(OP,ENDS,PREF,SCL) creates a fun for OP adaptively using the
>> preferences
>> % provided in the structure PREF (see chbfunpref).  Here SCL is a
>> structure
>> % with fields SCL.H (horizontal scale) and SCL.V (vertical scale).
>> %
>> % Additionally, exponents can be pass within PREF by attaching them in a
>> cell
>> % array to PREF.EXPS, and a non-adaptive call can be forced by setting
>> % PREF.N to be a positive integer.
>> %
>> % [G,ISH] = FUN(...) returns the constructed fun G and the boolean ISH,
>> % which is true if the construction is believed to have converged and
>> false
>> % otherwise.
>> %
>> % FUN creates an empty fun.
>> %
>> % See http://www.maths.ox.ac.uk/chebfun for chebfun information.
>>
>> %   Copyright 2002-2009 by The Chebfun Team.
>> %   Last commit: $Author: hale $: $Rev: 991 $:
>> %   $Date: 2009-12-16 16:06:29 +0000 (Wed, 16 Dec 2009) $:
>> ----------------------------------------------------------
>>
>> I repeat it would be nice if Chebfun would work in Octave!
>>
>>        Dan
>>
>
>
> Let's add it to the long list of things that would be nice, then :)
> The class support is far from complete. Some things simply don't work
> at all, in particular inheritance combined with nonscalar classes.
> This doesn't seem to be used here, so maybe a simple fix is possible,
> something with concatenation of classes.
>
> I agree that chebfun seems quite interesting, but as it apparently is
> a non-free software, I'm not much interested in making it work, and
> I'm not going to install it or use it. So, if you want to go on, I
> suggest:
>
> First try the development version. Only "binary safe" bugfixes are
> applied to the stable series, so chances are that the development
> sources can do better. If not, please try to reduce the problem to
> something simple. It seems something to do with class concatenation.
> If you can present a bug report that doesn't start with "install
> chebfun...", then I'll try to find the problem.
>
> regards
>
> --
> RNDr. Jaroslav Hajek, PhD
> computing expert & GNU Octave developer
> Aeronautical Research and Test Institute (VZLU)
> Prague, Czech Republic
> url: www.highegg.matfyz.cz
>
> The Cebfun license says:
> Redistribution of this software, with or without modification, is permitted
> provided that the following conditions are met:
>
> * Redistributions must retain the above copyright notice, this list of
> conditions and the following disclaimer.
>
> * Neither the name of Oxford University nor the names of the chebfun authors
> may be used to endorse or promote products derived from this software
> without specific prior written permission.
>
> * The software is not used commercially without prior written consent.
> Commercial use shall be defined as any use for which any financial return is
> received. This includes, but is not limited to, integration of all or part
> of the software into a product for sale or license by or on behalf of the
> licensee to third parties.
> ============================================
>

Yes, I've read this. The last paragraph makes it a non-free software.



-- 
RNDr. Jaroslav Hajek, PhD
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz