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From: Andrew on 7 Dec 2009 16:07
Three exact differential equations ... with simple by-hand solutions.

dsolve('2*x*y + (x^2 + y^2)*Dy = 0','x')
dsolve('1 + log(x) + 2*x*log(y) + (x^2/y - 2*y)*Dy = 0','x')
dsolve('Dy + (6*x^2*y + y^3 + 5*x^4)/(2*x^3 + 3*x*y^2 + 12*y^3)=0','x')

Matlab gives quite nutty answers ... one including the Wright omega function.

What am I doing wrong? This does not seem to be a case of some constant terms here and there that aren't 'summed up'.

Thanks for any insight!

Andrew
From: Andrew on 11 Dec 2009 06:15
"Andrew " <removethis(a)removethis.com> wrote in message <hfjqpl$sb4$1(a)fred.mathworks.com>...
> Three exact differential equations ... with simple by-hand solutions.
>
> dsolve('2*x*y + (x^2 + y^2)*Dy = 0','x')
> dsolve('1 + log(x) + 2*x*log(y) + (x^2/y - 2*y)*Dy = 0','x')
> dsolve('Dy + (6*x^2*y + y^3 + 5*x^4)/(2*x^3 + 3*x*y^2 + 12*y^3)=0','x')
>
> Matlab gives quite nutty answers ... one including the Wright omega function.
>
> What am I doing wrong? This does not seem to be a case of some constant terms here and there that aren't 'summed up'.
>
> Thanks for any insight!
>
> Andrew

Any of you experts out there able to help? Is this something that I shouldn't expect to work?
From: Andrew on 11 Dec 2009 10:31
"Andrew " <removethis(a)removethis.com> wrote in message <hft9k1$5hj$1(a)fred.mathworks.com>...
> "Andrew " <removethis(a)removethis.com> wrote in message <hfjqpl$sb4$1(a)fred.mathworks.com>...
> > Three exact differential equations ... with simple by-hand solutions.
> >
> > dsolve('2*x*y + (x^2 + y^2)*Dy = 0','x')
> > dsolve('1 + log(x) + 2*x*log(y) + (x^2/y - 2*y)*Dy = 0','x')
> > dsolve('Dy + (6*x^2*y + y^3 + 5*x^4)/(2*x^3 + 3*x*y^2 + 12*y^3)=0','x')
> >
> > Matlab gives quite nutty answers ... one including the Wright omega function.
> >
> > What am I doing wrong? This does not seem to be a case of some constant terms here and there that aren't 'summed up'.
> >
> > Thanks for any insight!
> >
> > Andrew
>
> Any of you experts out there able to help? Is this something that I shouldn't expect to work?

The correct answers are provided by the free Maxima by the way ... for example

depends(y,x);
(2*x^3 + 3*x*y^2 + 12 *y^3)*diff(y,x) + (6*x^2*y + y^3 + 5*x^4) = 0;
ode2(%,y,x);

Anyone spot something wrong? Or should I be just filing a bug report?
From: Steven Lord on 11 Dec 2009 13:35

"Andrew " <removethis(a)removethis.com> wrote in message
news:hftok5$rpb$1(a)fred.mathworks.com...
> "Andrew " <removethis(a)removethis.com> wrote in message
> <hft9k1$5hj$1(a)fred.mathworks.com>...
>> "Andrew " <removethis(a)removethis.com> wrote in message
>> <hfjqpl$sb4$1(a)fred.mathworks.com>...
>> > Three exact differential equations ... with simple by-hand solutions.
>> >
>> > dsolve('2*x*y + (x^2 + y^2)*Dy = 0','x')
>> > dsolve('1 + log(x) + 2*x*log(y) + (x^2/y - 2*y)*Dy = 0','x')
>> > dsolve('Dy + (6*x^2*y + y^3 + 5*x^4)/(2*x^3 + 3*x*y^2 + 12*y^3)=0','x')
>> >
>> > Matlab gives quite nutty answers ... one including the Wright omega
>> > function.
>> >
>> > What am I doing wrong? This does not seem to be a case of some constant
>> > terms here and there that aren't 'summed up'.
>> >
>> > Thanks for any insight!
>> >
>> > Andrew
>>
>> Any of you experts out there able to help? Is this something that I
>> shouldn't expect to work?
>
> The correct answers are provided by the free Maxima by the way ... for
> example
>
> depends(y,x);
> (2*x^3 + 3*x*y^2 + 12 *y^3)*diff(y,x) + (6*x^2*y + y^3 + 5*x^4) = 0;
> ode2(%,y,x);
>
> Anyone spot something wrong? Or should I be just filing a bug report?

Yes, please file a bug report via Technical Support.

--
Steve Lord
slord(a)mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ


From: Andrew on 11 Dec 2009 14:12
"Steven Lord" <slord(a)mathworks.com> wrote in message <hfu3b4$4c9$1(a)fred.mathworks.com>...
>
> "Andrew " <removethis(a)removethis.com> wrote in message
> news:hftok5$rpb$1(a)fred.mathworks.com...
> > "Andrew " <removethis(a)removethis.com> wrote in message
> > <hft9k1$5hj$1(a)fred.mathworks.com>...
> >> "Andrew " <removethis(a)removethis.com> wrote in message
> >> <hfjqpl$sb4$1(a)fred.mathworks.com>...
> >> > Three exact differential equations ... with simple by-hand solutions.
> >> >
> >> > dsolve('2*x*y + (x^2 + y^2)*Dy = 0','x')
> >> > dsolve('1 + log(x) + 2*x*log(y) + (x^2/y - 2*y)*Dy = 0','x')
> >> > dsolve('Dy + (6*x^2*y + y^3 + 5*x^4)/(2*x^3 + 3*x*y^2 + 12*y^3)=0','x')
> >> >
> >> > Matlab gives quite nutty answers ... one including the Wright omega
> >> > function.
> >> >
> >> > What am I doing wrong? This does not seem to be a case of some constant
> >> > terms here and there that aren't 'summed up'.
> >> >
> >> > Thanks for any insight!
> >> >
> >> > Andrew
> >>
> >> Any of you experts out there able to help? Is this something that I
> >> shouldn't expect to work?
> >
> > The correct answers are provided by the free Maxima by the way ... for
> > example
> >
> > depends(y,x);
> > (2*x^3 + 3*x*y^2 + 12 *y^3)*diff(y,x) + (6*x^2*y + y^3 + 5*x^4) = 0;
> > ode2(%,y,x);
> >
> > Anyone spot something wrong? Or should I be just filing a bug report?
>
> Yes, please file a bug report via Technical Support.
>
> --
> Steve Lord
> slord(a)mathworks.com
> comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ

Thanks, have done, Steve. At least I know it's not me making a mistake.

Cheers.
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