2020-04-02 23:32:16 +0200 received badge ● Notable Question (source) 2015-05-18 19:29:36 +0200 received badge ● Popular Question (source) 2013-05-31 16:27:23 +0200 commented answer Difficulty solving some second order differential equations Thank you so much. I can finally get my work done :) Is there a specific reason that it does not work with symbolic operations 2013-05-31 16:27:04 +0200 answered a question Difficulty solving some second order differential equations Thank you so much. I can finally get my work done :) Is there a specific reason that it does not work with symbolic operations 2013-05-31 15:40:21 +0200 received badge ● Student (source) 2013-05-31 15:26:04 +0200 received badge ● Scholar (source) 2013-05-31 15:26:04 +0200 marked best answer Difficulty solving some second order differential equations Concerning your first issue, instead of the symbolic solve() approach, you can use a numerical approach using the find_root() function: sage: find_root(diff(specificSolution,t),1e-6,5e-6) 3.6275987337046833e-06  This approach also works for your second issue: sage: find_root(specificSolution-Vin*0.1,0,1) 4.882292726784699e-07  Hence, you can check: sage: Vout,t = var("Vout,t") sage: L = 1e-3 sage: C = 1e-9 sage: Vin = 5 sage: R = 1e3 sage: Vout = function("Vout",t) sage: equation = L*C*diff(Vout,t,2) + R*C*diff(Vout,t) + Vout == Vin sage: specificSolution = desolve(equation,Vout,ivar=t,ics=[0,0,0]) sage: Max = find_root(diff(specificSolution,t),1e-6,5e-6) sage: M10 = find_root(specificSolution-Vin*0.1,0,1) sage: M90 = find_root(specificSolution-Vin*0.9,0,1) sage: plotMax = 2e-5 sage: plot1 = plot(specificSolution,[t,0,plotMax],rgbcolor=[0,0,0]) sage: plot1 += plot(Vin*0.1,[t,0,plotMax],rgbcolor=[0,0,1]) #10% line sage: plot1 += plot(Vin*0.9,[t,0,plotMax],rgbcolor=[0,1,0]) #90% line sage: plot1 += plot(specificSolution(t=Max),[t,0,plotMax],rgbcolor=[1,0,0]) sage: plot1 += line([(Max,0),(Max,6)],rgbcolor=[1,0,0]) sage: plot1 += line([(M10,0),(M10,6)],rgbcolor=[0,0,1]) sage: plot1 += line([(M90,0),(M90,6)],rgbcolor=[0,1,0]) sage: plot1  Which looks correct. 2013-05-31 15:26:03 +0200 received badge ● Supporter (source) 2013-05-31 13:51:05 +0200 asked a question Difficulty solving some second order differential equations I have trouble finding 10% and 90% of the rise time in a second order differential equation. I have tried to search but i have not solved my issue, so now i ask here. I have added the code to aleph.sagemath.org however the link is crazy long so i put it in a short link: http://bit.utoft.org/138hfAz The code is also on pastebin http://pastebin.com/4hwdLJuT Please help :) Cheers J. Utoft