MathGroup Archive 2002

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

Search the Archive

RE: Exponential forms and substitution

  • To: mathgroup at smc.vnet.net
  • Subject: [mg34490] RE: [mg34460] Exponential forms and substitution
  • From: "DrBob" <majort at cox-internet.com>
  • Date: Thu, 23 May 2002 03:32:42 -0400 (EDT)
  • Reply-to: <drbob at bigfoot.com>
  • Sender: owner-wri-mathgroup at wolfram.com

For the second problem, you could leave g undefined, but use a
substitution rule when you WANT it to have a value.  For instance, if we
want to compute acceleration due to the earth's gravity at various
distances (r) measured in earth radii, we might start with the basic
formula and a few rules:

a = -g/r^2;
earthGrav = g -> 9.80655 meter/Second^2;
moonDistance = r -> 384403/12756;
a // InputForm
-g/r^2

Acceleration at any radius, measured in earth radii:

a /. earthGrav // InputForm

(-9.80655*meter)/(r^2*Second^2)

Acceleration at the moon's orbit (approximate):

a /. {earthGrav, moonDistance} // InputForm

(-0.010798706345925642*meter)/ Second^2

These are not sophisticated examples, but maybe they'll give you ideas.

Bobby Treat

-----Original Message-----
From: Steve Gray [mailto:stevebg at adelphia.net] 
To: mathgroup at smc.vnet.net
Subject: [mg34490] [mg34460] Exponential forms and substitution

    For various reasons I have complex exponentials written
both as (for example) (-1)^(2/5) and the equivalent
E^(I Pi/5). How do I convert both forms into the same
form of my choice?
    Also I have a variable, say g, defined as (-1)^(2/5) . In
the complex matrices I work with it is important for visual
reasons to have the symbol g itself appear when I need it,
instead of one of its numeric equivalents. Using the usual
substitution rules as I understand them does not seem to
work.
    Any tips will be greatly welcomed!







  • Prev by Date: Re: silly newbie questions
  • Next by Date: Re: Problem with Precision?
  • Previous by thread: Re: Exponential forms and substitution
  • Next by thread: Re: Exponential forms and substitution