[CLN-list] Types in cl_R

[Isidro Cachadiña Gutiérrez]

El Jueves, 18 de Noviembre de 2004 13:13, Bruno Haible escribió:
> Isidro Cachadiña Gutiérrez wrote:
> > cl_R x,y,z;
> >
> > z=expt(x,y);
> >
> > I have problems with the prototypes defined in <real.h> that causes that
> > expt cannot be used in this way.
>
> If x is negative, the result can be a complex number. If you know a priori
> that the result will be real, you can use a checked cast:
>
>    z = As(cl_R)(expt(x,y));

>
> > I also can define this function as:
> >
> > cln::cl_R expt(cln::cl_R x, cln::cl_R y)
> > {
> >   return exp(x*ln(y));
> > }
>
> Actually this is the other way around: exp(x*ln(y)) is y^x, not x^y.
>
Correct.   Must be exp(y*ln(x)).

> By using 'ln' here, not the more general 'log', you have asserted that the
> base is > 0. No wonder you don't need a cast here.

Yes, of course.  I'm insterested on real functions depending on real 
arguments. 

Now, I have the same problem with functions like cos, acos, etc.  which 
depends on complex arguments, for example

cl_R acos (cl_R x ) is not defined you have to do something like

 realpart(acos(complex(x,0)))

or are there anything quicker and dirty ?.

> Bruno
>
>
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*                    Dr. Isidro Cachadiña Gutiérrez                       * 
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