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## Re: [Help-gsl] RK4 Help required

**From**: |
Simpson, Kenneth |

**Subject**: |
Re: [Help-gsl] RK4 Help required |

**Date**: |
Thu, 10 May 2007 09:45:17 -0700 |

If the charges are electrical charges, typically one looks
at the resultant force on one of charges due to the other
charges.
Hence, for a particular i, say i=1, one sums the forces on i
due to other j charges, namely, j=2,3,4.
And if you're looking for x(t) for the charges, you need to
write the the 2nd order force equation as two coupled 1st order
equations:
dv/dt=Columb's Law
dx/dt=v
-- Ken
cigdem ozkan wrote:
>* Hi again,*
>* I am posting a smaller version of my question rearding rk4 since I didnt get *
>* a reply and I am really anxious for some feedback.*
>
>* I have the following fuction:*
>* dxi/dt = k*qi*(xi-xj)/sqrt((xi-xj)2+(yi-yj)2+(zi-zj)2)*
>* where qi is the charge of the i-th particle, xi, yi, zi are the coordinates *
>* of the i-th particle and xj, yj,zj are the coordinates of the j-th particle. *
>* Input for the initial values: q[4] = { 1.0, 1.0, -1.0, 1.0 } charge x0[4] = *
>* { 1.0, 2.3, 3.2, 4.0 } init posn x*
>* y0[4] = { 1.0, 2.4, 3.0, 4.0 } init posn y*
>* z0[4] = { 1.0, 2.5, 3.3, 4.2 } init posn z*
>* QUESTION:*
>* Since there are two values for each coordinate (i and j), how can I write the *
>* function in an acceptable form for RK4? I would appreciate any feedback *
>* concerning RK4.*
>* Thanks for your time,*
>* C.*
>
>* ---------------------------------*
>* Ahhh...imagining that irresistible "new car" smell?*
>* Check outnew cars at Yahoo! Autos.*
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