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MathGroup Archive 2006

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RE: Problems solving using Solve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg68822] RE: [mg68809] Problems solving using Solve
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sun, 20 Aug 2006 04:43:40 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Akil,

Don't do so much in one step. When I plug your data into Cone there are
already problems. First make certain that the Cone routine is working and
giving you what you expect. If it isn't you could add Print statments in
Cone to see what is happening.

Also, I would calculate afg and look at it before plugging into the last
Solve statement.

Also, are you expecting afg to be calculated entirely symbolically? If you
define the data including centerOfMassy, then you couldn't differentiate
with respect to centerOfMassy.

If you have a problem you have to go back and make certain that each step is
working before putting it all together.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/

From: akil [mailto:akomur at wanadoo.nl]
To: mathgroup at smc.vnet.net


I have a problem suing the following code:

Cone[beta_, v_,rcAB_,rcCD_,ax_,ay_,cx_,cy_,centerOfMassx_,centerOfMassy_] :=
Module[
{betaUsed, vtemp, fx, fy, ex, ey,
waarde,criticalRC,criticalHeight,xVerplaatsing,ePx2Py2},
      betaUsed = beta ;
      vtemp = v;
      fline[x_] := Tan[betaUsed]x - Tan[betaUsed]vtemp;
      fx = x /. Solve[fline[x] == cd[x,rcCD,cx,cy], x][[1]];
      fy = cd[fx,rcCD,cx,cy];
      criticalRC = (centerOfMassy - fy)/(centerOfMassx - fx);
      criticalHeight = -criticalRC*fx + fy;
      ex = (-ay + rcAB*ax + criticalHeight)/(rcAB + (-criticalRC));
      ey = ab[ex,rcAB,ax,ay];
      xVerplaatsing = ex - vtemp;
      ePx2Py2 = Sqrt[xVerplaatsing^2 + ey^2];
      waarde = xVerplaatsing/ePx2Py2;
      ArcCos[-waarde]
];

afg =
Simplify[D[Cone[beta,v,rcAB,rcCD,ax,ay,cx,cy,centerOfMassx,centerOfMassy],v]
,
TimeConstraint -> 1 ];
Solve[afg== 0, v];

eg.
{ax,ay}= {-44.9376, 36.1678} and {cx,cy}= {17.8329, 122.477} and
{centerOfMassx,centerOfMassy}={-18.6338,72.3356} and rcAB=-0.166667 and
rcCD=-0.37931

Doing the Solve[afg== 0, v] takes ages (after an hour I quit it). Is there
any way I can make it work faster? Is any code in Cone such that it
unnecessarily makes it run faster? So are there any ways I can try to make
everything run faster? Using integers it runs, but it takes too long when
using real cones (made up of four points A B C D and a centerOfMass).

Akil




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