Mathematica 9 is now available
Student Support Forum
-----
Student Support Forum: 'Strange out put of DSolve' topicStudent Support Forum > General > Archives > "Strange out put of DSolve"

< Previous CommentHelp | Reply To Comment | Reply To Topic
Author Comment/Response
yehuda
02/03/13 04:03am

Well, the fact that you get an answer from Maple is not a guarantee to a good answer
Try adding a parameter to the ODE

sol = DSolve[y'[x] == Tan[x + y[x]] + a, y[x], x]

you get the result
Solve[y[x] - (-Log[(1 + a) Cos[x + y[x]] + Sin[x + y[x]]] + (1 + a +
a^2) (x + y[x]))/(2 + 2 a + a^2) == C[1], y[x]]

Now check the limit of the left hand side within the Solve command

Limit[sol[[1, 1]], a -> 0]
returning
1/2 (-x + Log[Cos[x + y[x]] + Sin[x + y[x]]] + y[x])

That is, Log[Cos[x+y[x]] may be undefined if Cos[x+y[x]] equals zero
What are the initial conditions ? say that for x==0 y[0] ==Pi/2, then what???

yehuda



URL: ,

Subject (listing for 'Strange out put of DSolve')
Author Date Posted
Strange out put of DSolve Shariel 02/02/13 11:50am
Re: Strange out put of DSolve yehuda 02/03/13 04:03am
< Previous CommentHelp | Reply To Comment | Reply To Topic