Re: Integrating functions with with constant arguments

[Geordie McBain]

On Tue, 2006-08-15 at 15:29 +1000, John Dalton wrote:
> QUESTION 1:
> 
> I'm trying to run the following function under octave:
> 
> function z = test_handle(t)
>    z   = quad(@(x) pow2(x, t), 0.5, 1);
> end
> 
> It is an integration with a constant argument in the integrand function.
> It works in Matlab, but octave 2.1.73 fails with the
> following error. 
> 
> error: `t' undefined

Try this idiom:

octave:5> global t;
octave:8> t = 1;
octave:9> function p = fun2 (x); global t; p = pow2 (x, t); endfunction
octave:10> function z = test_handle (); z = quad (@fun2, 0.5, 1);
endfunction
octave:11> test_handle
ans =  0.75000

The parameter t needs to be declared global inside the integrand
function.

> According to this post: 
> http://velveeta.che.wisc.edu/octave/lists/archive//octave-maintainers.2002/msg00110.html
> it should work.  I've also tried making 't' global ("global t") and
> also tried using a global intermediate variable between the argument t
> and its use as a  parameter to pow2.  If pow2 is replaced with a user
> defined function (say fun2) the code fails saying "fun2" is not
> defined.  It's as if the evaluation of quad's argument function is
> not seeing the parent's environment.
> 
> QUESTION 2:
> 
> As an aside, I also did the following test:
> 
> octave:5> global a=3;is_global('a')
> ans = 0
> 
> I would have though the answer should be '1'.
> 
> 
> Sorry if these are FAQs.  I have spent a day looking for an
> answer but have not found one (apart from the email above).
> Any help will be appreciated very much. (Thanks in advance.)
> 
> Regards
> John Dalton
> 
> 
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-- 
Geordie McBain
www.aeromech.usyd.edu.au/~mcbain