Re: Useless functions in matlab function library.

[Qingshan Chen]

I want to do one thing, and I found the way how to do it with inline.
Here is a little script:

%%%%%%%%%%%%Script starts%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% This script explore the fourier series expansion of a given
% function over the interval [x0,x1]. by plot the approximation series 
(to a given degree).

n=10; x0=-1; x1=1; dx=0.01;
tol=[1.0e-4,0];
thefunction = '(exp(x)+exp(-x))/2';
f = inline(thefunction);

x=x0:dx:x1; fx=zeros(1,size(x,1));
a=zeros(n,1); b=zeros(n,1);
a0=quad(f,x0,x1, tol)/(x1-x0);
len=x1-x0;
for k=1:n
   f1=@(x) f(x).*sin(2*k*pi*x/len);
   f2=@(x) f(x).*cos(2*k*pi*x/len);
   a(k) = quad(f1,x0,x1, tol)/(0.5*len);
   b(k) = quad(f2,x0,x1, tol)/(0.5*len);
end

fx=a0;
for k=1:n
   fx = fx + a(k)*sin(2*k*pi*x/len) + ...
        b(k)*cos(2*k*pi*x/len);
end

plot(x,fx, x, f(x));
title(['Fourier series expansion of the function ' thefunction]);

%%%%%%%%%%%%%%%%%%%%%Script ends%%%%%%%%%%%%%%%%%%%%%%%

Basically this script find and plot the fourier expansion of a given 
function, and then title
the plot with a string expression for the function. To plot another 
function, you just need to
change the string value for the variable thefunction, and at the end the 
expression for the
function will be updated in the title automatically. Can you do this 
with anonymous function only?
If yes, tell me how. I am quite new to both octave and matlab. So if you 
find me ignorant, please
don't shout at me:)


Guillem Borrell Nogueras wrote:
> I'm so sorry if starting a discussion in a help mailing list is completely 
> inappropiate...
>
> Thinking about the previous thread...
>
> Is the inline function just a bad, syntactically wrong anonymous function?  
> I've always criticized Matlab saying that it needs to seriously sanitize the 
> language. I find the inline function completely wrong, it's like an eval 
> function used to assign a function to a variable. And David just said that it 
> is even slow! (well, in Matlab).  Is the inline function used for any other 
> purpose than something that is much better done with an anonymous function? 
> (inlining code is a much broader concept)
>
> I taught a bit of matlab in my school of engineering.  I had only six hours to 
> taught as much matlab as possible and I never told my students about the 
> inline function. Instead, I spent more than an hour trying to make them 
> understand what a function handle is.
>
> Do you know any matlab function that is just rubbish?  What parts of matlab 
> you think that are completely wrong (like the object orientation 
> implementation)?
>
> guillem
>
> On Tuesday 10 July 2007 12:35, David Bateman wrote:
>   
> > Guillem Borrell Nogueras wrote:
> >     
> > > It is much better to use an anonymous function to fit this purpose.
> > >
> > > In this case would be:
> > >       
> > > > > k = 2
> > > > > f = @(x) k*x^2
> > > > >           
> > Well, for Matlab this is true, as the inline functions use Matlab's
> > object class whereas anonymous functions are in the matlab
> > parser/interpreter itself. So under Matlab anonymous functions are
> > significantly faster to use than inline functions. However, under Octave
> > inline functions are just a special type of anonymous functions and so
> > there is no speed disadvantage.
> >
> > That being said, yes it is still better to use anonymous functions as
> > then you'll have better performance if you share your code with users of
> > the other product... Also, the way "inline" finds what are the arguments
> > of the function are, is a horrible mess which Octave had to copy for
> > compatibility.  Anonymous functions have a much cleaner interface (i.e.
> > you are required to define the arguments)..
> >
> > D.
> >
> >     
> > > To make this thing work you must upgrade to octave 2.9.x.  In earlier
> > > versions of octave the anonymous function won't find the constant k.
> > >
> > > You can find more information about anonymous functions and function
> > > handles here:
> > > http://www.mathworks.com/access/helpdesk/help/techdoc/matlab.html. look
> > > for anonymous functions in the index.
> > >
> > > guillem
> > >       
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