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 Author Comment/Response bruce 04/22/05 07:29am I'm new to mathematica and have been using it to solve differential equations. Today i did a simple equation and managed to plot it (plot looked correct) but when i tried (and tried and tried...) to use Findroot to find the root i keep getting error messages. This is my work (without the plot): mc = 1; mp = 0.01; l1 = 0.1; l2 = 0.4; g = 9.81; d = (mc l1 - mp l2)*g/(mc l1^2 + mp l2^2) 81.1862 simpletreb = NDSolve[{ϕ''[ t] == -d Sin[ϕ[t]], ϕ[0] == (3π/4), ϕ'[0] == 0}, ϕ[t], {t, 0, 1}] {{ϕ[t] -> InterpolatingFunction[{{0., 1.}}, <>][t]}} {{ϕ[t] -> InterpolatingFunction[{{0.`, 1.`}}, "<>"][t]}} Plot[ϕ[t] /. simpletreb, {t, 0, 0.5}]; *PLOT GOES HERE* FindRoot[ϕ[t] == 0, {t,0.2}] Findroot::nlnum : The function value (ϕ[0.2]} is not a list of numbers with dimensions {1} at {t} = {0.2} ************* note: the "ϕ" is a symbol that won't show up here. Also attached is a screenshot of what i've done. I tried many things all of which came up with various errors. From the plot i know the root is between 0.25 and 0.3. If anyone can point me in right direction id greatly appreciate it! Attachment: findroot problem.JPG, URL: ,

 Subject (listing for 'findroot problem') Author Date Posted findroot problem bruce 04/22/05 07:29am Re: findroot problem yehuda ben-s... 04/25/05 01:43am
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