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MathGroup Archive 2003

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Re: DSolve and N do not commute

  • To: mathgroup at smc.vnet.net
  • Subject: [mg40267] Re: DSolve and N do not commute
  • From: Bill Rowe <listuser at earthlink.net>
  • Date: Fri, 28 Mar 2003 04:32:36 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

On 3/27/03 at 6:51 AM, selwynh at earthlink.net (Selwyn Hollis) wrote:

>Very strange... No such "bug" in Version 4.1.5 for Mac OS X:

>eq := (f''[r] + 8 2^(2/3)/3 f'[r] == -8 2^(1/3)/3 f[r])

>DSolve[eq, f[r], r]

>{{f[r] -> C[1]/E^((2/3)*2^(2/3)*r) + C[2]/E^(2*2^(2/3)*r)}}

>DSolve[N[eq], f[r], r]

>{{f[r] -> C[1]/E^(3.1748*r) + C[2]/E^(1.05827*r)}}

Interesting. In Version 4.2.1 for Mac OS X this last results in

{{f[r] -> C[1]/E^(3.1748*r) + (r*C[2])/E^(3.1748*r)}}


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