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References to other Issues or PRs Fixes sympy#19545 Brief description of what is fixed or changed The code `Order(1/n - 3/(3*n +2), (n, oo))` returns `1/n`, which is not a sharp result. As a consequence `Sum(1/n - 3/(3*n +2), (n, 1, oo)).is_convergent()` gives the wrong result `False`. In the lines 208-214 of `order.py`, if the number of variables are >= 2, then the expression is expanded and is handled in `expr.is_Add` case. However in the case of a single variable, the alghorithm for the other case seems better. Factorizing the expression forces to use the better alghoritm in the case of a single variable. See also PR#18340 On branch issue-19545 Changes to be committed: modified: sympy/concrete/tests/test_sums_products.py modified: sympy/series/order.py modified: sympy/series/tests/test_order.py
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Codecov Report
@@ Coverage Diff @@
## master #19546 +/- ##
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+ Coverage 75.664% 75.757% +0.093%
=============================================
Files 654 654
Lines 169939 170565 +626
Branches 40065 40423 +358
=============================================
+ Hits 128583 129216 +633
+ Misses 35740 35739 -1
+ Partials 5616 5610 -6 |
sympy/series/order.py
Outdated
| # expand()'ed expr (handled in "if expr.is_Add" branch below). | ||
| expr = expr.expand() | ||
| else: | ||
| expr = expr.factor() |
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It seems that this aims to transform the sum 1/x - 3/(3*x + 2) into a product, so it looks like it should only be applied to instances of Add. The code would probably be better placed here:
Lines 199 to 201 in f7318db
It is possible that expand_multinomial could be removed and replaced by this. You could also test something like
num, den = expr.as_numer_denom()
expr = num/den
instead of expr.factor() which may be more expensive.
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It seems that this aims to transform the sum 1/x - 3/(3*x + 2) into a product, so it looks like it should only be applied to instances of Add. The code would probably be better placed here:
sympy/sympy/series/order.py
Lines 199 to 201 in f7318db
if expr.is_Add:
from sympy import expand_multinomial
expr = expand_multinomial(expr)
Right. I changed the location of factor.
It is possible that expand_multinomial could be removed
Yes, I run the tests and they pass also without expand_multinomial.
You could also test something like
num, den = expr.as_numer_denom() expr = num/deninstead of expr.factor() which may be more expensive.
Putting this instead of expr.factor() causes 2 failures in tests. The tests which failure are:
test_wester.pyat lines 2088-2090.test_trigonometric.pyat llines 1224-1225.
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Putting this instead of
expr.factor()causes 2 failures in tests. The tests which failure are:
test_wester.pyat lines 2088-2090.test_trigonometric.pyat llines 1224-1225.
Can you tell what is expr in these cases using num/den and when you use expr.factor() ?
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For test_wester.
expr = -exp(-_p**2/(_p + 1) + _p)*exp(_p**2/(_p + 1) - _p)/2 - exp(-_p**2/(_p + 1) + _p)*exp(_p**2/(_p + 1) - _p)/(2*_p)
expr.factor() = -(_p + 1)/(2*_p)
num = -_p*exp(-_p**2/(_p + 1) + _p)*exp(_p**2/(_p + 1) - _p) - exp(-_p**2/(_p + 1) + _p)*exp(_p**2/(_p + 1) - _p)
den = 2*_p
In this case the test does not give an error, but it never finishes.
For test_trigonometric.
expr = -4*_Dummy_69 + (_Dummy_69 + 1)**4 - 4*(_Dummy_69 + 1)**3 + 6*(_Dummy_69 + 1)**2 - 3
expr.factor() = _Dummy_69**4
num = -4*_Dummy_69 + (_Dummy_69 + 1)**4 - 4*(_Dummy_69 + 1)**3 + 6*(_Dummy_69 + 1)**2 - 3
den = 1
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It looks like only factor factor will help here.
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Sphinx test failed though nothing was changed in the documentation. I'll try to restart it. |
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The restart button has vanished again. |
It will: #19551 |
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Closing and opening to restart the build. |
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Thanks, ready to be merged. |
5 participants
References to other Issues or PRs
Fixes #19545
Brief description of what is fixed or changed
The code
Order(1/n - 3/(3*n +2), (n, oo))returns1/n, whichis not a sharp result.
As a consequence
Sum(1/n - 3/(3*n +2), (n, 1, oo)).is_convergent()gives the wrong result
False.In the lines 208-214 of
order.py, if the number of variables are >= 2,then the expression is expanded and is handled in
expr.is_Addcase.However in the case of a single variable,
the alghorithm for the other case seems better.
Factorizing the expression forces to use the better alghoritm in the case
of a single variable.
modified: sympy/concrete/tests/test_sums_products.py
modified: sympy/series/order.py
modified: sympy/series/tests/test_order.py
Other comments
See also #18340
Release Notes