       Re: 2 Assumptions for one parameter?

• To: mathgroup at smc.vnet.net
• Subject: [mg128053] Re: 2 Assumptions for one parameter?
• From: Bill Rowe <readnews at sbcglobal.net>
• Date: Wed, 12 Sep 2012 02:58:04 -0400 (EDT)
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• Delivered-to: l-mathgroup@wolfram.com
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```On 9/11/12 at 2:32 AM,
=?ISO-8859-1?Q?Andreas_Talmon_l=27Arm=E9e?= at smc.vnet.net wrote:

>What is the right typing to make two assumptions for one parameter?
>Something like this:

>\$Assumptions={a>0&&Element[a,Reals]}

either what you have or:

\$Assumpitions={a>0, Element[a,Reals]}

but note, by default Mathematica makes a variable as general as
possible. So, since a>0 isn't meaningful for complex a, it follows:

\$Assumptions={a>0&&Element[a,Reals]}
\$Assumptions={a>0, Element[a,Reals]}
\$Assumptions={a>0}

all achieve exactly the same thing.

>And is there a way to to control my assumptions made for the
>parameters I use something like

>?a

It is unclear to me what you are trying to do here. Setting the
value of \$Assumptions impacts those functions that look at the
value of \$Assumptions when you use them but has no effect on the
value of other symbols such as a. That is you can do:

In:= Clear[a]; \$Assumptions = {a > 0};
Simplify@Element[Sqrt[a], Reals]

Out= True

work with it

In:= a = -2;
Element[Sqrt[a], Reals]

Out= False

but this definitely causes problems for functions that look at
the value of \$Assumptions since now

In:= Simplify@Element[Sqrt[a], Reals]

Out= True

and generates an warning stating one or more assumptions
evaluated to False

```

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