Re: FindRoot & NDSolve

*To*: mathgroup at smc.vnet.net*Subject*: [mg64683] Re: [mg64650] FindRoot & NDSolve*From*: Pratik Desai <pdesai1 at umbc.edu>*Date*: Mon, 27 Feb 2006 00:18:32 -0500 (EST)*References*: <200602250753.CAA13936@smc.vnet.net> <44008AE9.6070708@umbc.edu> <44008C23.1030205@umbc.edu>*Sender*: owner-wri-mathgroup at wolfram.com

Pratik Desai wrote: > Pratik Desai wrote: > >> Takashi Inoue wrote: >> >>> Hi all, >>> >>> This is my first post to here. >>> I have a problem and want your help. >>> >>> Mathematica 4 did the following calculation with no pleblem, >>> while Mathematica 5(.2) cannot do it. >>> >>> FindRoot[ >>> (f /.NDSolve[ {D[f[x], {x,1}] - 2 x - a == 0, f[0] == 0}, f, {x, -3, >>> 3} ][[1]])[2] == 4, >>> {a, -10, 10} >>> ] >> >> >> I think FindRoot requires a initial guess in 5.X and you need some >> kind of looping for your different values of a >> >> >> Here are two possible alternatives (that I could think of) using >> DSolve and NDSolve >> >> (*Using DSolve (more preferable perhaps because of the closed form >> nature)*) >> >> TableForm[{#,x/.FindRoot[(f/.DSolve[{D[f[x], {x,1}]== 2 x + #, f[0] >> == 0}, f, >> x][[1,1]])[x]==4,{x,1}]//N}&/@Range[-10,10,1],TableHeadings->{Automatic,{"a","Root >> for f[x,a]"}}] >> >> (*Using NDSolve ) >> >> Clear[f,x,a] >> Table[Reap[NDSolve[{D[f[x], {x,1}]== 2 x + a, f[0] == 0}, f, >> {x,-3,3}, Method->{EventLocator, >> "Event"->f[x]-4,"EventAction":>Sow[{a,x}]}],{a,-10,10,1}] > > > There is an error in the above code for NDSolve, here is the correct one > Table[NDSolve[{D[f[x], {x,1}]== 2 x + a, f[0] == 0}, f, {x,-3,3}, > Method->{EventLocator, > "Event"->f[x]-4,"EventAction":>Print[{a,x}]}],{a,-10,10,1}]; There is an even bigger error (in comprehension) :-[ sorry about that! Pratik > > > >> >> >> Hope this helps >> >> Pratik >> >>> Takashi Inoue,Dept. Phys. Sophia University >> >> >> >> >> >

**References**:**FindRoot & NDSolve***From:*Takashi Inoue <takash-i@sophia.ac.jp>