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MathGroup Archive 2004

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Re: DSOLVE in 5.01 ??

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47623] Re: DSOLVE in 5.01 ??
  • From: "Peter Pein" <petsie at arcor.de>
  • Date: Sun, 18 Apr 2004 04:15:26 -0400 (EDT)
  • References: <c5j82s$r3h$1@smc.vnet.net> <c5oaui$1fl$1@smc.vnet.net> <c5qj6n$fvp$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"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
-- 
Peter Pein, Berlin
to write to me, start the subject with [







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