[Date Index]
[Thread Index]
[Author Index]
Re: global real variables
*To*: mathgroup at smc.vnet.net
*Subject*: [mg22059] Re: global real variables
*From*: adam_smith at my-deja.com
*Date*: Fri, 11 Feb 2000 02:38:44 -0500 (EST)
*References*: <87trds$5o3@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
Naum,
What you need to do in the case of Conjugate[] is to use the command
ComplexExpand[ Conjugate[ x + x * p^-1 ]] as explained in the help this
assumes that all the variables are real. (You can specify a list that
says that some variables are complex.) ComplexExpand[] is very useful
when dealing with complex numbers of the form a + b I. The following
examples are very illustrative. Note the use of TargetFunctions->
{Re,Im}. This "forces" the output in the form of a real + imaginary
part.
In[1]:=
z = a + b I
Out[1]=
a + I*b
In[2]:=
z*Conjugate[z]
Out[2]=
(a + I*b)*Conjugate[a + I*b]
In[3]:=
ComplexExpand[z*Conjugate[z]]
Out[3]=
a^2 + b^2
In[7]:=
z/Conjugate[z]
Out[7]=
(a + I*b)/Conjugate[a + I*b]
In[8]:=
ComplexExpand[z/Conjugate[z]]
Out[8]=
a^2/Abs[a + I*b]^2 + (2*I*a*b)/Abs[a + I*b]^2 - b^2/Abs[a + I*b]^2
In[6]:=
ComplexExpand[z/Conjugate[z], TargetFunctions -> {Re, Im}]
Out[6]=
a^2/(a^2 + b^2) + (2*I*a*b)/(a^2 + b^2) - b^2/(a^2 + b^2)
Adam Smith
In article <87trds$5o3 at smc.vnet.net>,
Naum Phleger <naum at cava.physics.ucsb.edu> wrote:
> I asked a dumb question a few weeks ago about making variables
real and
> found that Mathematica 4 took care of this better. I have been using
it
> since. I still have a couple of problems with it though. First, I
can have
> variables be treated as real by using the assumption Element[x,Reals]
in a
> simplify command, but I want x to be real in all commands so I don't
have to
> keep using Simplify each time I want x to be recognized as real.
Second,
> even this doesn't seem to work quite right. Here is what I mean.
>
> Say I have tow var.s, x and p. Both are real so I can do this.
>
> Simplify[ Conjugate[ x ] , Element[ x , Reals ] ] ----> x
>
> amd I get the same thing for p, but it stops working if I have
functions of
> x and p, for instance I get
>
> Simplify[ Conjugate[ x + x * p^-1 ] , Element[ {x,p} , Reals ] ] ----
>
>
> Conjugate[ x + x * p^-1 ]
>
> It works if I use FullSimplify AND put p^-1 into the list of
variables
> that I want to have real. How can I get around this without listing
every
> negative power of every variable and wasting time with FullSimplify.
Thanks
> for any help. Thanks.
>
> -NAUM
>
>
Sent via Deja.com http://www.deja.com/
Before you buy.
Prev by Date:
**Re: Dealing with irregular shaped arrays**
Next by Date:
**Simplifying expressions for use in C programs**
Previous by thread:
**Re: global real variables**
Next by thread:
**Re: global real variables**
| |