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DSolve differences?

  • To: mathgroup at
  • Subject: [mg33283] DSolve differences?
  • From: michael_chang86 at (Michael Chang)
  • Date: Wed, 13 Mar 2002 03:14:55 -0500 (EST)
  • Sender: owner-wri-mathgroup at

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

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,


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