Problem with differential equation (DESOLVE)
03-03-2015, 05:29 PM
Post: #1
 ZellAllon Junior Member Posts: 4 Joined: Feb 2015
Problem with differential equation (DESOLVE)
Hello,

I don't know why when I try to solve a Homogeneous differential equation my hp prime I get something like:

desolve((y') = ((y/x)+(x/y)),y) = [pnt[G_0*e^((1/2)*_(t38)^2),G_0*_(t38)*e^((1/2)*_(t38)^2)]]

the solution must be Y^2=X^2*LN(X^2)+C*X^2

03-03-2015, 06:59 PM (This post was last modified: 03-03-2015 07:12 PM by salvomic.)
Post: #2
 salvomic Senior Member Posts: 1,394 Joined: Jan 2015
RE: Problem with differential equation (DESOLVE)
(03-03-2015 05:29 PM)ZellAllon Wrote:  Hello,

I don't know why when I try to solve a Homogeneous differential equation my hp prime I get something like:

desolve((y') = ((y/x)+(x/y)),y) = [pnt[G_0*e^((1/2)*_(t38)^2),G_0*_(t38)*e^((1/2)*_(t38)^2)]]

the solution must be Y^2=X^2*LN(X^2)+C*X^2

see here: Parisse replied to me few time ago...

the "strange" expression should be like
$y=c*e^{\frac{t^{2}}{2}} \ AND \ y=c*t*e^{\frac{t^{2}}{2}}$

G_0 ok for "c", but, yes, "_t38" is a bit bizzarre, and we are lucky that it is not "p38"

Note also that $$e^{\frac{t^{2}}{2}}$$ is simply $$\sqrt{e^{t^{2}}}$$ ...

∫aL√0mic (IT9CLU) :: HP Prime 50g 41CX 71b 42s 39s 35s 12C 15C - DM42, DM41X - WP34s Prime Soft. Lib
03-04-2015, 10:07 AM
Post: #3
 parisse Senior Member Posts: 1,208 Joined: Dec 2013
RE: Problem with differential equation (DESOLVE)
You get parametric solutions currently. With Xcas current CAS version, you would get
[√2*x*√(ln(x/G_0)),-√2*x*√(ln(x/G_0))]
03-04-2015, 04:49 PM
Post: #4
 ZellAllon Junior Member Posts: 4 Joined: Feb 2015
RE: Problem with differential equation (DESOLVE)
(03-03-2015 06:59 PM)salvomic Wrote:
(03-03-2015 05:29 PM)ZellAllon Wrote:  Hello,

I don't know why when I try to solve a Homogeneous differential equation my hp prime I get something like:

desolve((y') = ((y/x)+(x/y)),y) = [pnt[G_0*e^((1/2)*_(t38)^2),G_0*_(t38)*e^((1/2)*_(t38)^2)]]

the solution must be Y^2=X^2*LN(X^2)+C*X^2

see here: Parisse replied to me few time ago...

the "strange" expression should be like
$y=c*e^{\frac{t^{2}}{2}} \ AND \ y=c*t*e^{\frac{t^{2}}{2}}$

G_0 ok for "c", but, yes, "_t38" is a bit bizzarre, and we are lucky that it is not "p38"

Note also that $$e^{\frac{t^{2}}{2}}$$ is simply $$\sqrt{e^{t^{2}}}$$ ...
ok, understood, thanks.But how can I take these parametric solutions and get y as a function of x?
03-04-2015, 05:44 PM
Post: #5
 ZellAllon Junior Member Posts: 4 Joined: Feb 2015
RE: Problem with differential equation (DESOLVE)
(03-04-2015 10:07 AM)parisse Wrote:  You get parametric solutions currently. With Xcas current CAS version, you would get
[√2*x*√(ln(x/G_0)),-√2*x*√(ln(x/G_0))]

Hello,

How do you get that solution? explain to me please!
03-04-2015, 06:09 PM
Post: #6
 Tim Wessman Senior Member Posts: 2,280 Joined: Dec 2013
RE: Problem with differential equation (DESOLVE)
(03-04-2015 05:44 PM)ZellAllon Wrote:  How do you get that solution? explain to me please!

That is the author of the CAS inside Prime. He is using the pc version (which is newer then the current version in Prime) and that result is returned. If/Until that code is put into the Prime firmware the calculator will continue to return the result you posted.

TW

Although I work for HP, the views and opinions I post here are my own.
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