Re: Integration with constants?

[Søren Hauberg]

You also need to make alpha global inside your function. So you function 
 should look something like this:

function res = Ji1(x)
   global alpha; ## This line is the only difference
   res = log( ...
     ( sqrt(1 + alpha.^2 + 2.*alpha.*cos(x)) + 1 + alpha.*cos(x) ) ./ ...
     ( sqrt(1 + alpha.^2 + 2.*alpha.*cos(x)) + alpha.*sin(x) - 1 ) )
end

I haven't tested it, but I think it should help...

Søren

Jens Benecke skrev:
> John W. Eaton wrote:
>
> > | > | [J2, ier, nf,   err] = quad(@(x) log( ...
> > | > |         sqrt(1 + alpha.^2 + 2.*a.pha.*cos(2.*x)) + alpha + cos(2.*x)
> > | > |         ), 0, pi/2, 1e-6)
> > | > | "alpha" is a constant that has been calculated before. However,
> > | > | Octave tells me "error: alpha undefined ..."
>
> > | Sorry ... 2.1.72, on SuSE Linux.
> > | Any way to do this with the 2.1 branch?
> >
> > In that case, I think the only option is a separate function and
> > global variables.
>
> Hi,
>
> I tried this - setting "alpha" to global, then executing my function:
>
> 38 global alpha = R2./R1                -> returns 1.2286
> 39 kii = sqrt(4.*alpha ./ (1+alpha).^2) -> works fine
> 40 
> 41 isglobal('alpha')                    -> returns 1
> 42 function res = Ji1(x) 
> 43    res = log( ...
> 44      ( sqrt(1 + alpha.^2 + 2.*alpha.*cos(x)) + 1 + alpha.*cos(x) ) ./ ...
> 45      ( sqrt(1 + alpha.^2 + 2.*alpha.*cos(x)) + alpha.*sin(x) - 1 ) )
> 46 end
> 47 
> 48 [J1, ier, nf, err] = quad('Ji1(x)', 0, pi/2, 1e-6)
>
>
> Result:
>
> error: `alpha' undefined near line 44 column 13
> error: evaluating binary operator `.^' near line 44, column 18
> error: evaluating binary operator `+' near line 44, column 11
> error: evaluating binary operator `+' near line 44, column 22
> error: evaluating argument list element number 1
> error: evaluating binary operator `+' near line 44, column 42
> error: evaluating binary operator `+' near line 44, column 46
> error: evaluating binary operator `./' near line 44, column 64
> error: evaluating argument list element number 1
> error: evaluating assignment expression near line 43, column 5
> error: called from `Ji1'
> error: evaluating assignment expression near line 48, column 34
> error: called from `__quad_fcn_Q__'
> error: quad: evaluation of user-supplied function failed
>
>
> I'm a bit lost here... =;()