#3510 another example of odeL returning spurious result for incorrect inputs

[Daniel Volinski]

Hi All,

Consider the following code:

load(odes)$load(contrib_ode)$

assume(R_s>0)$
declare(R_s,constant)$

Eq:'diff(y,r,1) = (R_s * y)/(2 * r * (r-R_s));

sol1:odeL(Eq,y,r),fullratsimp;
method;
ode_check(Eq,sol1),fullratsimp;

sol2:ode2(Eq,y,r),fullratsimp;
method;
is(ev(Eq,sol2,diff,eval,fullratsimp));

method;
ode_check(Eq,sol3);

method;
ode_check(Eq,sol4);

The results of odeL are wrong.

Daniel

[Daniel Volinski]

This bug has not been addressed yet.
Daniel

[Aleksas]

odeL is function for solving linear ode with constant coefficients in form
L(y)=f.
Tray:
(%i2) eq:'diff(y,r,1) = (R_s * y)/(2 * r * (r-R_s))$
ode2(eq,y,r),radcan;
(%o2) y=(%c*sqrt(r-R_s))/sqrt(r)

best

2019-01-12, št, 19:42 Daniel Volinski danielvolinski@users.sourceforge.net
rašė:

This bug has not been addressed yet.
Daniel

---

• [bugs:#3510] https://sourceforge.net/p/maxima/bugs/3510/ odeL wrong
  results*

Status: open
Group: None
Created: Sun Dec 16, 2018 07:25 AM UTC by Daniel Volinski
Last Updated: Sun Dec 16, 2018 07:25 AM UTC
Owner: nobody

Hi All,

Consider the following code:

load(odes)$load(contrib_ode)$

assume(R_s>0)$
declare(R_s,constant)$

Eq:'diff(y,r,1) = (R_s * y)/(2 * r * (r-R_s));

sol1:odeL(Eq,y,r),fullratsimp;
method;
ode_check(Eq,sol1),fullratsimp;

sol2:ode2(Eq,y,r),fullratsimp;
method;
is(ev(Eq,sol2,diff,eval,fullratsimp));

method;
ode_check(Eq,sol3);

method;
ode_check(Eq,sol4);

The results of odeL are wrong.

Daniel

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[Daniel Volinski]

I understand, thank you.
I still think that odeL should issue an error if it can't solve the equation, instead of issuing a wrong answer.
Daniel

[Robert Dodier]

See also #3511 which is another example of the same issue.