Make checkodesol work for series solutions

[oscarbenjamin]

References to other Issues or PRs

Fixes #16000

Brief description of what is fixed or changed

Makes checkodesol work for series solutions of ODEs as returned by dsolve. I'm not sure this works for series solutions around non-zero points because dsolve doesn't yet return correct series solution around nonzero points.

Other comments

I'm still working on this...

Release Notes

• solvers
  • checkodesol now works for series solutions of ODEs.

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• solvers
  • checkodesol now works for series solutions of ODEs. (#17588 by @oscarbenjamin)

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#### References to other Issues or PRs
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Fixes #16000 

#### Brief description of what is fixed or changed

Makes checkodesol work for series solutions of ODEs as returned by dsolve. I'm not sure this works for series solutions around non-zero points because dsolve doesn't yet return correct series solution around nonzero points.

#### Other comments

I'm still working on this...

#### Release Notes

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* solvers
    * checkodesol now works for series solutions of ODEs.
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Update

The release notes on the wiki have been updated.

[codecov]

Codecov Report

Merging #17588 into master will decrease coverage by 0.005%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##           master    #17588       +/-   ##
============================================
- Coverage   74.76%   74.754%   -0.006%     
============================================
  Files         634       634               
  Lines      165333    165347       +14     
  Branches    38857     38858        +1     
============================================
+ Hits       123604    123605        +1     
- Misses      36309     36319       +10     
- Partials     5420      5423        +3

[RituRajSingh878]

O((x+2)**6) has a different meaning. So we can't get from the solution and also O(x**6) is the correct way of representing the solution.

In [9]: Order((x+2)**6)
Out[9]: O(1)

For the checkodesol We can pass the argument x0 and then we can use it for your work.

[oscarbenjamin]

What I meant is:

In [1]: O((x+2)**6, (x, -2))                                                                                                      
Out[1]: 
 ⎛       6        ⎞
O⎝(x + 2) ; x → -2⎠

[oscarbenjamin]

Making dsolve return that fails because constantsimp calls cse which absorbs all the terms #17587

[oscarbenjamin]

I'll merge this soon if no one objects