Re: help me plz
- To: mathgroup at smc.vnet.net
- Subject: [mg32163] Re: [mg32149] help me plz
- From: BobHanlon at aol.com
- Date: Mon, 31 Dec 2001 02:24:21 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
In a message dated 12/29/01 6:31:44 PM, samer_ghamrawui at hotmail.com writes:
>i want to solve this equation
>
>y"*y'+2y"'=0
>
>y(0)=0
>y'(0)=0
>y'(infini)=1
>
Off[Solve::ifun];
Clear[y];
eqns = {y''[x]*y'[x]+2y'''[x]==0, y[0]==0};
soln = DSolve[eqns, y[x], x]//Flatten
{y[x] -> 4*Log[Cosh[(x*Sqrt[C[1]])/
2]]}
The condition, y'[0] == 0 is redundant
D[y[x] /. soln, x] == 0 /. x -> 0
True
Solve[Simplify[
D[y[x] /. soln, x] /. x -> Infinity,
C[1] > 0]==1, C[1]]
{{C[1] -> 1/4}}
y[x_] := 4*Log[Cosh[x/4]];
And@@Join[eqns,{y'[0]==0,y'[Infinity]==1}]
True
Bob Hanlon
Chantilly, VA USA