Re: error with function handles

[Martin Helm]

Am Mittwoch, 19. August 2009 14:50:34 schrieb simone marras:
> Hi everyone, thanks for helping.
>
> I corrected the errors that you pointed out but still obtained exactly
> the same error that I would get initially. To summarize the steps,
> this is what we have:
>
> 1)
>
> >> function y = fun(x)
> >>
>  >   y = 10*exp(-50.0*abs(x));
> >
> >    endfunction
>
> 2)
>
> function int = midpntc(a, b, m, fun)
>
>       h=(b-a)/m
>       x=[a+h/2:h:b];
>
>       k = max(size(x));
>
>       y = fun(x);
>
>       if size(y) == 1, y = diag(ones(k))*y; end
>
>       int = h*sum(y);
> end
>
> 3) And finally, call to midpntc as:
>
> octave:72> midpntc(0, 1,10, @fun)
> h =  0.10000
> error: octave_base_value::convert_to_str_internal (): wrong type
> argument `function handle'
> error: eval: expecting std::string argument
> error: evaluating assignment expression near line 13, column 4
> error: called from `midpntc' in file
> `/home/simone/Documents/scientific/CFD/myCFD_library/ATMOSPHERE_miscellanea
>/TMP/midpntc.m'
>
>
> I am lost
> S.
>
> On Wed, Aug 19, 2009 at 2:45 PM, Martin Helm<address@hidden> wrote:
> > Am Mittwoch, 19. August 2009 14:18:30 schrieb simone marras:
> >> Hi,
> >>
> >> I am trying to call a function that accepts a function handle as
> >> argument. My functions are all defined within the same directory where
> >> myfun.m rerturns a simple expression as:
> >>
> >> function y = myfun(x)
> >>      y = 10*exp(-50.0*abs(x)) - 0.01/((x-0.5).*(x-0.5) + 0.001) +
> >> 5.0*sin(5.0*x);
> >> endfunction
> >>
> >> and midpntc is defined as:
> >>
> >> function [Int] = midpntc(a, b, m, function)
> >>
> >>     h=(b-a)/m
> >>       x=[a+h/2:h:b];
> >>
> >>       k = max(size(x));
> >>       y = eval(fun);
> >>
> >>       if size(y) == 1, y = diag(ones(k))*y; end
> >>
> >>       int = h*sum(y);
> >>
> >> when I call midpntc in octave as:
> >> >> Int = midpntc(0, 1, 10, "myfun")
> >>
> >> I obtain the following error:
> >>
> >>  midpntc(0,1,10,"myfun")
> >> h =  0.10000
> >> error: `x' undefined near line 2 column 9
> >> error: evaluating binary operator `.^' near line 2, column 10
> >> error: evaluating binary operator `-' near line 2, column 13
> >> error: evaluating binary operator `-' near line 2, column 17
> >> error: evaluating binary operator `./' near line 2, column 6
> >> error: evaluating assignment expression near line 2, column 3
> >> error: called from `myfun'
> >> error: evaluating assignment expression near line 13, column 4
> >> error: called from `midpntc' in file
> >> `/home/simone/Documents/scientific/CFD/myCFD_library/ATMOSPHERE_miscella
> >>nea /TMP/midpntc.m'
> >>
> >>
> >> while, if I use the syntax
> >>
> >> >> Int = midpntc(0, 1, 10, @myfun)
> >>
> >> the error that I get is:
> >>
> >> h =  0.10000
> >> error: octave_base_value::convert_to_str_internal (): wrong type
> >> argument `function handle'
> >> error: eval: expecting std::string argument
> >> error: evaluating assignment expression near line 13, column 4
> >> error: called from `midpntc' in file
> >> `/home/simone/Documents/scientific/CFD/myCFD_library/ATMOSPHERE_miscella
> >>nea /TMP/midpntc.m'
> >>
> >>
> >> Could anyone help me with this issue?
> >> Thank you very much in advance,
> >>
> >> S.
> >
> > Hello,
> >
> > if you really want to pass the function name as string you should use
> > feval instead of eval to evaluate it.
> >
> > y = feval(fun, x);
> >
> > Or you simply use a function handle instead of a string
> >
> > midpntc(0,1,10,@myfun)
> >
> > and in midpntc
> >
> > y = fun(x);
> >
> > instead of eval
> >
> > Hope that helps.
> >
> > - mh


>From your error message I can see that your function still uses eval

> error: octave_base_value::convert_to_str_internal (): wrong type

So it seems your updated version of midptnc did not come into effect.
Try 
clear midpntc
to delete the old function definition which seems to persist in your RAM.

- mh