ImageSet now supports multiple sets #14145
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sympy/sets/dispatchers.py
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| @dispatch(FunctionUnion, Intersection) | ||
| def function_sets(f, x): | ||
| return Intersection(imageset(f, arg) for arg in x.args) |
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Intersection of image sets may contain elements that are not in the image of the intersection. Compare the intersection of f([-1, 0]) and f([0, 1]) with the image of the intersection f({0}) when f(x) = x**2.
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I see. This code was just copied from the _eval_imageset method of Intersection. It is supposed to be called when the intersection cannot be calculated.
Shall we leave the imageset unevaluated for this case?
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Bijective functions may be treated separately.
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Shall we leave the imageset unevaluated for this case?
I guess that is what has to be done.
| # TODO: find a better condition for invertible functions: | ||
| if ((f in (exp, log)) # functions known to be invertible | ||
| or (fdiff > 0) == True or (fdiff < 0) == True # monotonous funcs | ||
| ): |
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@jksuom I put these conditions of invertibility. solveset needs this mapping to solve equations with Abs and similar. It does not look that clean.
Do we have a better way to test the invertibility of functions?
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We probably should have a method for testing invertibility in a set such as the union of x.args.
Additionally,
imagesethas been remapped to use multipledispatching.