DSolve differences?
- To: mathgroup at smc.vnet.net
- Subject: [mg33283] DSolve differences?
- From: michael_chang86 at hotmail.com (Michael Chang)
- Date: Wed, 13 Mar 2002 03:14:55 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
Hi everyone,
I'm a former user of Mathematica 3.0.x, and a current user of
Mathematica 4.1 for Windoze XP.
In the past, when I used Mathematica 3.0.x, I've been able to type:
In[1]:= DSolve[{y''[x]==c (y'[x])^2/y[x],y[0]==y0,y'[0]==y1},y[x],x]
and get a general closed form solution. Here, variable 'c' is
supposed to lie in [0,1], and y0 and y1 are both assumed to be Real
numbers.
In Mathematica 4.1, however, I get:
Solve::"tdep": "The equations appear to involve the variables to be
solved for in an essentially non-algebraic way."
DSolve::"bvfail": "For some branches of the general solution, unable
to solve the conditions."
However, version 4.1 will yield a result if I drop the initial
conditions ... namely, if I use
In[2]:= DSolve[{y''[x]==c (y'[x])^2/y[x]},y[x],x]
or if I *do* use the initial conditions, but with a specific value of
c ... for instance, c->1/3.
Okay, so I know that I can go in and try and back substitute and solve
for the integration constants C[1] and C[2] which occur in Out[2], but
I was wondering why version 3.0.x seems to handle this, but not the
(improved) 4.1?
As always, this newsgroup's help would be greatly appreciated!
Many thanks,
Michael