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MathGroup Archive 2006

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Re: General--Differential equation problem..

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66302] Re: [mg66284] General--Differential equation problem..
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Mon, 8 May 2006 00:46:54 -0400 (EDT)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

Clear[z];
With[{r=2},z=z/.DSolve[{z'[s] == 1/r,z[0]==0},z, s][[1]]];

Clear[x,y];
{x,y}={x,y}/.DSolve[
        {x'[s]==Cos[z[s]], y'[s]==Sin[z[s]],x[0]==0,y[0]==0}, {x, y}, s][[1]];

{x[s],y[s],z[s]}

{2*Sin[s/2], -2*(Cos[s/2] - 1), s/2}

With[{r=2},{x'[s] == Cos[z[s]], y'[s] == Sin[z[s]], z'[s] == 1/r}]

{True,True,True}

Table[ParametricPlot[{x[s], y[s]}, {s, 0, smax},
      PlotRange->{{-2.1,2.1},{-0.1,4.1}},Frame->True,Axes->False],
    {smax,Pi/6,4Pi,Pi/6}];


Bob Hanlon

---- randomtalk at gmail.com wrote: 
> hello, i was trying to solve a set of differential equations needed for a school project.. However, i'm completely new to mathematica 5.0, and i have downloaded trial, here is what i inputed into the software:
> 
> In[2]:=
> DSolve[{x'[s] == Cos[z], y'[s] == Sin[z], z'[s] == 1/r, r == 2}, {x, y, z}, s]
> 
> returns this error: DSolve::dvnoarg: The function z appears with no arguments.
> 
> Is there anything wrong with what i inputed? The differential equations came from this website: http://fy.chalmers.se/LISEBERG/eng/loop_pe.html
> 
> Link to the forum page for this post:
> http://www.mathematica-users.org/webMathematica/wiki/wiki.jsp?pageName=Special:Forum_ViewTopic&pid=10212#p10212
> Posted through http://www.mathematica-users.org [[postId=10212]]
> 
> 


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