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Re: Re: Solve inconsistant actions?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87257] Re: [mg87217] Re: Solve inconsistant actions?
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sat, 5 Apr 2008 04:25:51 -0500 (EST)
  • Reply-to: hanlonr at cox.net

newrent = Table[125000 E^(r 14), {r, .01, .04, .005}];

The only case with a problem (its algorithms couldn't find a solution) is

Solve[#/rate == 1894000, rate] & /@ newrent // Column

{{rate->0.0759156}}
{}
{}
{{rate->0.0936555}}
{}
{{rate->0.107729}}
{{rate->0.115541}}



I find that simplifying an expression can sometimes help. 

Solve[Simplify[#/rate == 1894000], rate] & /@ newrent // Column

{{rate->0.0759156}}
{{rate->0.0814201}}
{{rate->0.0873238}}
{{rate->0.0936555}}
{{rate->0.100446}}
{{rate->0.107729}}
{{rate->0.115541}}



This is equivalent to what you did with

Solve[# == 1894000 rate, rate] & /@ newrent

Alternatively, use only exact or only approximate numbers (as in one of your examples). Hence, either

Solve[Simplify[#/rate == 1894000.], rate] & /@ newrent // Column

or

Solve[#/rate == 1894000, rate] & /@ Rationalize[newrent, 0] // N // Column

And Reduce has more robust capabilities than Solve


Bob Hanlon

---- mhicks <mhicks at san.rr.com> wrote: 
> Can someone enlighten me as to what discriminators Solve uses in 
> providing some solutions while disdaining others in the attached simple 
> code?
>  
> Is it an operator or Mathematica bug? I am running 6.0.1 under win xp.
> 
> 
> newrent = Table[125000 \[ExponentialE]^(r 14), {r, .01, .04, .005}] // N
> 
> Table[Solve[newrent[[i]]/rate == 1894000 , rate], {i, 1, 7}]
> 
> Table[Solve[newrent[[i]]/rate == 1894000. , rate], {i, 1, 7}]
> 
> Table[Reduce[newrent[[i]]/rate == 1894000 , rate], {i, 1, 7}]
> 
> Table[Solve[newrent[[i]] == 1894000 rate, rate], {i, 1, 7}]
> 
>  
>  Thanks for any help,
>  
>  Marlyn Hicks
>  
>  mhicks at san.rr.com
> 
> 



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