#17445: Missing documentation of derivative operator/notation
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Reporter: schymans | Owner:
Type: enhancement | Status: new
Priority: major | Milestone: sage-6.5
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: schymans | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by eviatarbach):
I think it is worth distinguishing. The standard counterexample to
equality of mixed partials is `f(x, y) = x*y*(x^2 - y^2)/(x^2 + y^2)`,
with `f(0, 0) = 0`, which is a continuous function but the second
derivatives at (0, 0) are unequal. This may not come about often in
practice (it doesn't seem like we can run this example without having
multivariable piecewise functions), but especially if people are using the
formal functions it should have correct mathematical properties.
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Ticket URL: <http://trac.sagemath.org/ticket/17445#comment:17>
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