       Re: Surprising DSolve problem

• To: mathgroup at smc.vnet.net
• Subject: [mg123979] Re: Surprising DSolve problem
• Date: Tue, 3 Jan 2012 05:29:47 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201201020742.CAA09063@smc.vnet.net>

```Sam,

Mathematica is deficient in this area.
(Hopefully they'll improve this someday)

Use it to solve
y''[x] + (2 y[x])/(Cosh[x]^2) == 0
for y and then substitute x->x/a for a solution to
y''[x] + (2 y[x])/(a^2 Cosh[x/a]^2) == 0

Cheers,

-----Original Message-----
From: Sam Takoy
Sent: Sunday, January 01, 2012 11:42 PM
To: mathgroup at smc.vnet.net
Subject: [mg123979] Surprising DSolve problem

Hi,

I find that my Mathematica (8.0.1)

can do

DSolve[ y''[x] + (2 y[x])/(Cosh[x]^2) == 0, y, x]

but can't do

DSolve[ y''[x] + (2 y[x])/(a^2 Cosh[x/a]^2) == 0, y, x] (*Additional
constant "a")

If I am not mistaken, the equations are equivalent by a trivial change
of variables.

What's going on here?

Thanks,

Sam

```

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