Open rtoy opened 4 months ago
rtoy
commented
4 months ago Imported from SourceForge on 2024-07-08 20:13:46 Created by billingd on 2016-09-24 02:44:03 Original: https://sourceforge.net/p/maxima/bugs/3036/#be69
rtoy
commented
4 months ago Imported from SourceForge on 2024-07-08 20:13:50 Created by aleksasd on 2016-09-24 04:45:34 Original: https://sourceforge.net/p/maxima/bugs/3036/#be69/e986
Solve y' = 1/x^2, y(inf)=0.
Solve y'' = 1/x^3, y(inf)=0, y'(inf)=0.
(%i2) eq1:'diff(y,x)=1/x^2$ eq2:'diff(y,x,2)=1/x^3$
(%i5) ode2(eq1,y,x); ic1(%,x=a,y=0); limit(%,a,inf); (%o3) y=%c-1/x (%o4) y=(x-a)/(a*x) (%o5) y=-1/x
(%i8) ode2(eq2,y,x); ic2(%,x=a,y=0,diff(y,x)=0); limit(%,a,inf); (%o6) y=%k2x+1/(2x)+%k1 (%o7) y=x/(2a^2)+1/(2x)-1/a (%o8) y=1/(2*x)
Other solution with odes: (%i9) load(odes)$
(%i11) ode1_ic(eq1,y,x,[a,0]); limit(%,a,inf); (%o10) y=(x-a)/(a*x) (%o11) y=-1/x
(%i13) ode2_ic(eq2,y,x,[a,0,0]); limit(%,a,inf); (%o12) y=x/(2a^2)+1/(2x)-1/a (%o13) y=1/(2*x)
best
Aleksas D
2016-09-24 5:44 GMT+03:00 David Billinghurst billingd@users.sf.net:
- assigned_to: David Billinghurst
- [bugs:#3036] https://sourceforge.net/p/maxima/bugs/3036/ Incorrect solution of ODEs "inf"*
Status: open Group: None Labels: ic1 ic2 inf Created: Tue Oct 20, 2015 05:13 PM UTC by sslavi Last Updated: Tue Oct 20, 2015 05:21 PM UTC Owner: David Billinghurst Attachments:
- ic1 ic2 inf bug.wxmx https://sourceforge.net/p/maxima/bugs/3036/attachment/ic1%20ic2%20inf%20bug.wxmx (1.5 kB; application/octet-stream)
Maxima seem to consider "inf" as a constant and hence doesn't solve correctly initial value problems involving "inf". The problem is present in both ic1 and ic2 functions. Please take a look at the attached example.
For your convenience, this is the transcript of the session:
Input: *> f1: 'diff(y,x)=1/x^2$
ode2(f1,y,x); ic1(%,x=inf,y=0);
- Output:> (%o2) y=%c-1/x (%o3) y=(x-inf)/(infx) the correct answer is 1/(2x).
Input: *> f2: 'diff(y,x,2)=1/x^3$
ode2(f2,y,x); ic2(%,x=inf,y=0,diff(y,x)=0);
- Output:>(%o5) y=%k2x+1/(2x)+%k1 (%o6) y=x/(2inf^2)+1/(2x)-1/inf the correct answer is 1/(2x).
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Imported from SourceForge on 2024-07-08 20:13:45 Created by sslavi on 2015-10-20 17:13:38 Original: https://sourceforge.net/p/maxima/bugs/3036
Maxima seem to consider "inf" as a constant and hence doesn't solve correctly initial value problems involving "inf". The problem is present in both ic1 and ic2 functions. Please take a look at the attached example.
For your convenience, this is the transcript of the session:
Input: *> f1: 'diff(y,x)=1/x^2$
Input: *> f2: 'diff(y,x,2)=1/x^3$
Attachments: