Added hyperbolic function in undetermined coefficients #18410
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Codecov Report
@@ Coverage Diff @@
## master #18410 +/- ##
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+ Coverage 75.284% 75.302% +0.017%
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Files 633 633
Lines 166951 166951
Branches 39397 39397
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+ Hits 125688 125718 +30
+ Misses 35729 35693 -36
- Partials 5534 5540 +6 |
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@oscarbenjamin can you review this? |
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What happens if the rhs includes both a hyperbolic function and exp(x)? Does it get confused? We should add a test for this. |
sympy/solvers/tests/test_ode.py
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| eq = f(x).diff(x, 2) - 49*f(x) - sinh(3*x) | ||
| sol = Eq(f(x), C1*exp(-7*x) + C2*exp(7*x) - sinh(3*x)/40) | ||
| assert sol == dsolve(eq) |
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Since these ODEs can already be solved on master these tests should specify the hint as in hint='nth_..._undetermined_coefficients'.
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What happens if the rhs includes both a hyperbolic function and exp(x)? Does it get confused? We should add a test for this.
It treats them seperately and i have added test for this .
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| def test_issue_18408(): | ||
| eq = f(x).diff(x, 3) - f(x).diff(x) - sinh(x) | ||
| sol = Eq(f(x), C1 + C2*exp(-x) + C3*exp(x) + x*sinh(x)/2) |
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It would be nice to have a solution in terms of sinh and cosh in this case, but that might not be straightforward to implement.
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I've often thought the same about exp(I*x) in some cases that would be preferred rather than cos/sin e.g.:
In [15]: dsolve(f(x).diff(x, 2) + f(x) - exp(I*x))
Out[15]:
ⅈ⋅x
ⅈ⋅x⋅ℯ
f(x) = C₁⋅sin(x) + C₂⋅cos(x) - ────────
2 Maybe there should be a parameter to dsolve to influence which type of solutions it generates.
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I think it could at least be smarter based on what sorts of functions are present in the ODE itself. But this can be done in a future PR.
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@oscarbenjamin does this look good? |
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Yes, looks good. |
4 participants
References to other Issues or PRs
Fixes #18408
Brief description of what is fixed or changed
Earlier the ode involving hyperbolic function were not classified by
nth_linear_constant_coeff_undetermined_coefficientsnot it is fixedOther comments
Release Notes
dsolvecan solve linear non-homogeneous ODEs involving hyperbolic functions when using the method of undetermined coefficients.