Re: Result to DEQ with WA versus Step-by-Step Yields

*To*: mathgroup at smc.vnet.net*Subject*: [mg132311] Re: Result to DEQ with WA versus Step-by-Step Yields*From*: amzoti <amzoti at gmail.com>*Date*: Fri, 7 Feb 2014 08:08:27 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net*References*: <20140201055416.D6FE16A13@smc.vnet.net> <lckifh$1gr$1@smc.vnet.net>

On Saturday, February 1, 2014 8:44:33 PM UTC-8, Bob Hanlon wrote: > The step-by-step solution provides the result for t >= 0 > > > > > > sol = ((WolframAlpha[ > > "v''+10 v'+125 v=250 unitstep(t),v(0)=0,v'(0)=25", > > {{"DifferentialEquationSolution", 1}, "Output"}] // > > ReleaseHold)[[1]]) // ToRules > > > > > > {v[t] -> ((5/2)*Sin[10*t])/E^(5*t) + > > (((-(5/2))*Sin[10*t])/E^(5*t) + > > ((1/2)*(4*E^(5*t) - 4*Cos[10*t] + 3*Sin[10*t]))/ > > E^(5*t))*UnitStep[t]} > > > > > > > > Simplify[sol, t >= 0] > > > > > > {v[t] -> 2 - (2*Cos[10*t])/E^(5*t) + > > ((3/2)*Sin[10*t])/E^(5*t)} > > > > > > > > Bob Hanlon > > > > > > On Sat, Feb 1, 2014 at 12:54 AM, amzoti <amzoti at gmail.com> wrote: > > > > > When you solve this DEW using WA, you get a result. > > > > > > However, when you click step-by-step, the result is different. > > > > > > Is this a bug? > > > > > > v'' + 10 v' + 125 v = 250 unitstep(t), v(0) = 0, v'(0) = 25 > > > > > > Thanks > > > > > > Thanks all! Bob Hanlon: I see that you reply to many posting with excellent feedback. I have always wondered (as your posts are different than many in a very good way), how did you learn Mathematica so well? What approach and/or references did you use? Regards -A