[Date Index]
[Thread Index]
[Author Index]
Re: DSolve difficulties ...
*To*: mathgroup at smc.vnet.net
*Subject*: [mg111874] Re: DSolve difficulties ...
*From*: Slide <wdflannery at aol.com>
*Date*: Mon, 16 Aug 2010 05:55:33 -0400 (EDT)
*References*: <i45rdj$g3o$1@smc.vnet.net> <i48jgi$e46$1@smc.vnet.net>
On Aug 15, 7:36 am, Helen Read <h... at together.net> wrote:
> On 8/14/2010 6:33 AM, Slide wrote:
>
> > Yesterday I typed in the following command line, into the student
> > version of Mathmatica .
>
> > DSolve[y''[x] == 1/(y[x]*y[x]), y[x], x]
>
> > and got a complicated Solve command and expression back with the
> > comment 'The equations appear to involve the variables to be solved
> > for in an essentially non-algebraic way.'
>
> Adding to my previous post:
>
> OK, the solution to DSolve comes out like this:
>
> Solve[((1/(C[1]^(3/2)))
> Log[-2 + 2 (C[1] + Sqrt[C[1]] Sqrt[C[1] - 2/y[x]]) y[x]] + (
> Sqrt[C[1] - 2/y[x]] y[x])/C[1])^2 == (x + C[2])^2, y[x]]
>
> That is, Mathematica is able to solve the differential equation, but the
> solution is given implicitly, rather than solved for y[x]. It got to the
> part where it wants to solve for y[x] in terms of x, can't do it, and
> quits there.
>
> If you then evaluate the output (the Solve[ ] ), you will get the
> message about "essentially non-algebraic" which is Mathematica's way of
> saying it cannot solve the equation explicitly. (It would have to begin
> with, if it could.)
>
> --
> Helen Read
> University of Vermont
Hi Helen,
Thanks for your response. Yep, that's what I got for a solution. Is
it possible for me to get Mathematica to explain, or at least list,
the steps it used to arrive at that solution? Note that had I
remembered to put a minus constant in front of the right side of the
differential equation, it would be the world's first, that is, the
differential equation for a falling object acted on by gravity in one
dimension ! ...... Newton's first DE, and it's a bear !
Prev by Date:
**Re: DSolve difficulties ...**
Next by Date:
**Re: "in-program" backup facility**
Previous by thread:
**Re: DSolve difficulties ...**
Next by thread:
**Re: DSolve difficulties ...**
| |