Re: DSolve Issues
- To: mathgroup at smc.vnet.net
- Subject: [mg88389] Re: [mg88335] DSolve Issues
- From: "W_Craig Carter" <ccarter at mit.edu>
- Date: Sat, 3 May 2008 06:19:44 -0400 (EDT)
- References: <200805020742.DAA05399@smc.vnet.net>
Hello,
I can't see your code, so I have to guess what you wish to do.
There is a difference between
0.
and
0
And for good and useful reasons
For your case:
Rationalize[ 0.104479, .00001] (*is 7/67*)
DSolve[Phi''[r] + 2*r^(-1) Phi'[r] + (7/67) Phi[r] == 0 , Phi[r], r]
gives a useful solution
Even more useful is
DSolve[Phi''[r] + 2*r^(-1) Phi'[r] + ArbitraryConstant Phi[r] == 0 , Phi[r], r]
On Fri, May 2, 2008 at 3:42 AM, donkorgi12
<ringtailinblacklw02 at gmail.com> wrote:
> I am solving the following Differential Equation
>
> Phi''[r]+2*r^(-1)Phi'[r]+0.104479*Phi[r]==0 and Phi[0]==K (some
> constant) ; kinda has a cos/sin solution
>
> Yet, Mathematica treats those "zeros" as something else.
>
Try this little experiment, it is very instructive for your zero
conceptualization (observe the "." in the output)
matsym = {{1, 1}, {10^24, 10^24}}
Det[matsym]
matnum = {{1., 1}, {10^24, 10^24}}
Det[matnum]
matnumappx = {{1., 1}, {10^24 + 1, 10^24}}
Det[matnumappx]
matappxsym = {{1, 1}, {10^24 + 1, 10^24}}
Det[matappxsym]
--
W. Craig Carter
- References:
- DSolve Issues
- From: donkorgi12 <ringtailinblacklw02@gmail.com>
- DSolve Issues