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MathGroup Archive 2002

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RE: Solve weirdness

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35032] RE: [mg35001] Solve weirdness
  • From: "DrBob" <majort at cox-internet.com>
  • Date: Thu, 20 Jun 2002 02:13:41 -0400 (EDT)
  • Reply-to: <drbob at bigfoot.com>
  • Sender: owner-wri-mathgroup at wolfram.com

The second ^ in that line of code looks like a typo; it caused an error
message.  When I eliminated that, the results were an error message and
the following answer:

Solve[{k*0.01^p == 10, 
   k*0.1 == 1}, {k, p}]

Solve::ifun:Inverse functions are being used by Solve, so some solutions
may 
not be found.

{{k -> 10., p -> 0.}}

Your answer doesn't satisfy the first condition, even if I've
misinterpreted the second:

k*.01^p == 10 /. {{k -> 10., p -> -1.}}

{False}

If I add a p to the second condition rather than eliminating ^, the
following returns unevaluated with an error message:

Solve[{k*0.01^p == 10, k*0.1^p == 1}, {k, p}]

Solve::tdep: The equations appear to involve the variables to be solved
for 
in an essentially non-algebraic way.

Solve[{0.01^p*k == 10, 0.1^p*k == 1}, {k, p}]

However, if that second reading of the problem is correct, and if we
eliminate approximations, here's a solution:

Off[Solve::"ifun"]
eqns = {k*(1/100)^p == 10, k*(1/10)^p == 1};
Solve[#/eqns[[2, 1]] & /@ eqns[[1]], k]
Solve[eqns[[2]] /. %, p]
{k, p} //. Flatten[{%, %%}]

{{k -> 10^(1 + 2*p)}}
{{p -> -1}}
{1/10, -1}

Perhaps we're using different Mathematica versions; I'm using 4.1 for Windows.

Bobby Treat


-----Original Message-----
From: Joshua A. Solomon [mailto:J.A.Solomon at city.ac.uk] 
To: mathgroup at smc.vnet.net
Subject: [mg35032] [mg35001] Solve weirdness

shouldn't

Solve[{k*.01^p==10,k*.1^==1},{k,p}]

produce

{{k->10.,p->-1.}}

? it doesn't. it produces

{{}}

. what's up with that?

js
-- 
Joshua A. Solomon
Department of Optometry and Visual Science
City University
London EC1V 0HB
Voice: (44) 20 7040 0192
Fax: (44) 20 7040 0182
J.A.Solomon at city.ac.uk
http://www.staff.city.ac.uk/~solomon






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