Ok, thank you for your answer. Now I understood.
Regards,
Michele
Il 26/07/2012 16:40, Jaime Villate ha scritto:
> On 07/26/2012 09:11 AM, Jaime Villate wrote:
>> On 07/25/2012 07:26 PM, Michele Minelli wrote:
>>> I was trying to plot y=abs(log(x)) with
>>>
>>> /plot2d(abs(log(x)), [x, -10, 10]);/
>>>
>>> and I realized that Maxima plots a curve even for x less than zero.
>>> Could someone explain me why (I remember reading it once but I
>>> couldn't find it anymore) and how to disable this representation if
>>> I want?
>> Hi,
>> that issue has been discussed in this list and I thought we had
>> decided to use the plot option plot_realpart with a default value of
>> false (that is what the manual says too); however, the plot_realpart
>> option is no longer being accepted by plot2d. I will investigate
>> what's going on; I might be responsible for this bug :(
> Please ignore my previous message. The option plot_realpart is working
> fine. For instance, try:
> plot2d(log(x), [x, -10, 10]);
> (default value 'false' for plot-realpart)
>
> plot2d(log(x), [x, -10, 10], [plot_realpart,true]);
>
> The function you were attempting to plot, abs(log(x)) is a real
> function, with a real value for any real x different from zero and as
> Raymond told you, if you don't want to see the part for x<0 you should
> not use the domain [x,-10,10].
>
> Notice that if x is real and less than zero, Maxima will give you the
> main-branch value:
> log(x) = log(abs(x)) + %i*%pi
> and abs() for a complex argument will give you the modulus of the
> complex number:
> abs(log(x)) = sqrt( log(abs(x))^2 + %pi^2)
>
> Regards,
> Jaime
>