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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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