```Date: Dec 7, 2012 1:37 AM
Author: Bob Hanlon
Subject: Re: System of differential equations

The Sin functions must be entered as Sin vice sin. The range of t istoo large to be handled.s = NDSolve[{    ph1''[t] + ph1'[t] + Sin[ph1[t]] - mu[t] - mu'[t] == 0.005,    ph2''[t] + ph2'[t] + Sin[ph2[t]] + mu[t] + mu'[t] == 0.005,    0.2 mu'[t] + mu[t] == ph1'[t] - ph2'[t], ph2[0] == 0, ph1[0] == 0,    ph2'[0] == 0, ph1'[0] == 0, mu[0] == 0},   {ph1[t], ph2[t], mu[t]},   {t, 0, 240}];Plot[Evaluate[Tooltip[#, ToString[#]] & /@    {ph1[t], ph2[t], mu[t]} /. s], {t, 0, 10}, Frame -> True, Axes -> False]However, the range on t affects the resultss = NDSolve[{    ph1''[t] + ph1'[t] + Sin[ph1[t]] - mu[t] - mu'[t] == 0.005,    ph2''[t] + ph2'[t] + Sin[ph2[t]] + mu[t] + mu'[t] == 0.005,    0.2 mu'[t] + mu[t] == ph1'[t] - ph2'[t], ph2[0] == 0, ph1[0] == 0,    ph2'[0] == 0, ph1'[0] == 0, mu[0] == 0},   {ph1[t], ph2[t], mu[t]},   {t, 0, 100}];Plot[Evaluate[Tooltip[#, ToString[#]] & /@    {ph1[t], ph2[t], mu[t]} /. s], {t, 0, 10}, Frame -> True, Axes -> False]Bob HanlonOn Thu, Dec 6, 2012 at 4:58 AM,  <hazem.abdelhafiz@gmail.com> wrote:> Dear all,> I want to solve this system of equations but I always get an error>> NDSolve::ndnum:Encountered non-numerical value for a derivative at t==0>> can any one help me on this>> s=NDSolve[{> ph1''[t]+ph1'[t]+sin[ph1[t]]-mu[t]-mu'[t]==0.005,> ph2''[t]+ph2'[t]+sin[ph2[t]]+mu[t]+mu'[t]==0.005,> 0.2mu'[t]+mu[t]==ph1'[t]-ph2'[t],> ph2[0]==0,> ph1[0]==0,> ph2'[0]==0,> ph1'[0]==0,> mu[0]==0> },> {ph1[t],ph2[t],mu[t]},> {t,0,5000}> ]>> thanks in advance,>
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