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MathGroup Archive 1998

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Re: calculation (Perhaps Solve could do more with rational exponents???)


  • To: mathgroup@smc.vnet.net
  • Subject: [mg12062] Re: calculation (Perhaps Solve could do more with rational exponents???)
  • From: "Wendy Hartman" <wendytangoalephzero@worldnet.att.net>
  • Date: Fri, 24 Apr 1998 01:52:32 -0400
  • Organization: AT&T WorldNet Services
  • References: <6gr69a$8lo@smc.vnet.net>

Solve[r^(5/2)/((r^(1/2)-1)^(1/3))==a,r] results in roots of a 15th order
polynomial (taking only a fraction of a second), while
Solve[r^(5/2)/((r^(1/3)-1)^(1/3))==a,r] had to be abended for spending
far more time and memory than seemed reasonable (Pentium II 266MHz w/
128 MBytes).  Making an "obvious" transformation
Solve[x^(15/2)/((x-1)^(1/3))==a,x]
results in roots of a 45th order polynomial (taking only a fraction of a
second)

To (my)(IMHO etc) human eyes both equations seem of "equal"
complexity... could Solve be extended to be more aggressive with
expressions involving rational powers???

Saeed Esmaily Rashid <saeedr@stud.ntnu.no> wrote in article
<6gr69a$8lo@smc.vnet.net>...
> Hello!
> 
> My name is Saeed and i'm studying physics. I have a problem which ihope
> someone can help me with it. I have an equation
> 
> .001422409738*R^(73/80)*(R^(1/2)-1)^(-13/40) == .04
> 
> i'm using the Solve function in Mathematica 3.0 to solve it for R, but
> it calculats endlessly and takes very long time. the question is that
> is there any way to optimize this equation or using another function in
> Mathematica 3.0 to make it faster to calculate?
> 
> Regards 
> 
> 
> 



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