How to replace some variables and how to solve a differential equation?
- To: mathgroup at smc.vnet.net
- Subject: [mg132359] How to replace some variables and how to solve a differential equation?
- From: bluesaturn <bluesaturn.at.kellnerweg.de at gmail.com>
- Date: Thu, 20 Feb 2014 03:27:39 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- Delivered-to: l-mathgroup@wolfram.com
- Delivered-to: mathgroup-outx@smc.vnet.net
- Delivered-to: mathgroup-newsendx@smc.vnet.net
Dear all,
I am really new to Mathematica.
I have two questions, please.
1. How to replace a variable in a function?
I have defined:
f[r_] := Log[((2*\[Lambda])/(\[Kappa]*r*
Cos[\[Lambda]*Log[(r/RM)]]))^2]
RM, lambda >0
I want to replace r with u given by
u=log[Kappa*r]
I did it by hand but whant to check my result.
2. How to check or solve the differential equation:
f"[u]=0.5*exp[2*u+f[u]]
It would be sufficient for me to insert f[u] and see if both sides are
the same. So far I failed.
Thank you for your help.
Regards
Blue