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MathGroup Archive 2004

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Re: DSOLVE in 5.01 ??

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47642] Re: DSOLVE in 5.01 ??
  • From: turbo cyx <turbocyx at gmx.net>
  • Date: Tue, 20 Apr 2004 03:18:46 -0400 (EDT)
  • References: <c5j82s$r3h$1@smc.vnet.net> <c5oaui$1fl$1@smc.vnet.net> <c5qj6n$fvp$1@smc.vnet.net> <c5ten8$hum$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

So its since 4.1, does this change anything??
and no, I am not steve_H
Cu
Cyx


On Sun, 18 Apr 2004 08:36:56 +0000 (UTC), "Peter Pein"
<petsie at arcor.de> wrote:

>"turbo cyx" <turbocyx at gmx.net> schrieb im Newsbeitrag
>news:c5qj6n$fvp$1 at smc.vnet.net...
>> Why should I bother with this?? I am not willing to use workarounds
>> for Wolfram bugs (I am coauthor of a widely used courseware in
>> austria. Now I have to write this workaround for all the Lessons wich
>> use DSolve and boundary conditions, in a few month when 6.0 finally is
>> available I can undo this again ....)
>> Mathematica 4.2 (and all previous version) has been able to solve this
>system,
>> so I think 5.01 should be also (BTW: 6.0 Alpha can solve this system
>> again)
>> Wolfram where is a bugfix
>> Cyx
>>
>Mathematica 4.0 must have been published after vers. 4.2:
>
>In[1]:=
>$Version
>dgl1 = m*g - c*v[t]^2 == m*Derivative[1][v][t];
>dgl2 = Derivative[1][s][t] == -v[t];
>DSolve[{dgl1, dgl2, s[0] == h0, v[0] == 0}, {s[t], v[t]}, t]
>Out[1]=
>4.0 for Microsoft Windows (July 16, 1999)
>From In[1]:=
>Solve::incnst:
>   Inconsistent or redundant transcendental equation. After
>                                             Sqrt[g] Sqrt[m] C[2] 2
>     reduction, the bad equation is 1 - Cosh[--------------------]
>                                                   Sqrt[c]
>     == 0.
>From In[1]:=
>Solve::incnst:
>   Inconsistent or redundant transcendental equation. After
>                                             Sqrt[g] Sqrt[m] C[2] 2
>     reduction, the bad equation is 1 - Cosh[--------------------]
>                                                   Sqrt[c]
>     == 0.
>From In[1]:=
>Solve::tdep: The equations appear to involve the variables to be
>    solved for in an essentially non-algebraic way.
>From In[1]:=
>DSolve::dsing:
>   Unable to fit initial/boundary conditions {s[0] == h0, v[0] == 0}
>     .
>Out[4]=
>{}
>In[5]:=
>DSolve[{dgl1,v[0]==0},v[t],t]
>Out[5]=
>                               Sqrt[c] Sqrt[g] t
>          Sqrt[g] Sqrt[m] Tanh[-----------------]
>                                    Sqrt[m]
>{{v[t] -> ---------------------------------------}}
>                          Sqrt[c]
>In[6]:=
>Integrate[-v[t]/.%[[1]],{t,0,z}]+h0
>Out[6]=
>                Sqrt[c] Sqrt[g] z
>     m Log[Cosh[-----------------]]
>                     Sqrt[m]
>h0 - ------------------------------
>                   c
>
>please check your statements _before_ posting (b.t.w. are you known as
>steve_H in sci.math.symbolic?).
>
>Thanks


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