       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:= DSolve[{y''[x]==c (y'[x])^2/y[x],y==y0,y'==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:= 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 and C which occur in Out, 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

```

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