Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1999
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1999

[Date Index] [Thread Index] [Author Index]

Search the Archive

Exponential Function and Expand

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18114] Exponential Function and Expand
  • From: Blimbaum Jerry DLPC <BlimbaumJE at ncsc.navy.mil>
  • Date: Thu, 17 Jun 1999 12:26:45 -0400
  • Delivery-date: Thu Jun 17 15:53:31 1999
  • Sender: owner-wri-mathgroup at wolfram.com

	In mg: 18029 Drago Ganic wrote:

	"Why Mathematica automatically expand E^u E^v to E^(u+v) but never
the inverse situation, i.e.
	E^(u+v) to E^u E^v.  In my textbooks I find that the relation
a^(u+v) = a^u a^v is valid for any a, u, v, (also Complex numbers) except a
= 0..."

	One response stated the importance of transforming a^b*a^c into
a^(b+c) because of its importance for many transformations.  I wanted to add
the example that suppose u = a and v = -a, hence E^a E^-a transforms to
E^(a+(-a)) = E^0 = 1.  If you did it the other way you end up with E^a*E^-a
which really doesnt do you any good.  However, in order to show that
Mathematica, in fact, does that I typed in the following:

	u = a;    v = -a;
	Expand[E^u*E^v]//TracePrint

	with the expectation that at some point I would see the
transformation  E^(a-a) by which Mathematica would get E^0 , hence the
output 1.   But to my surprise the last few outputs were:

	E^a*E^-a

	E^-a*E^a

	1

	Expand[1]

	1

	So where does the transformation a^b*a^c into a^(b+c) occur??    Why
did Mathematica simply change the order of the exponentials and then come up
with a value of 1 rather then showing the explicit addition of a + (-a) =
0??   Also, why would it try to Expand a number?

	THANKS.   Jerry Blimbaum    NSWC  Panama City, Fl

  • Prev by Date: Re: A little problem with positive numbers
  • Next by Date: Physical constants and their evaluation
  • Previous by thread: Reading in equations for evaluation
  • Next by thread: Physical constants and their evaluation