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  2. Differential structure - Wikipedia

    en.wikipedia.org/wiki/Differential_structure

    In particular, a C k-atlas that is C 0-compatible with a C 0-atlas that defines a topological manifold is said to determine a C k differential structure on the topological manifold. The C k equivalence classes of such atlases are the distinct C k differential structures of the manifold. Each distinct differential structure is determined by a ...

  3. Closed and exact differential forms - Wikipedia

    en.wikipedia.org/wiki/Closed_and_exact...

    In mathematics, especially vector calculus and differential topology, a closed form is a differential form α whose exterior derivative is zero (dα = 0), and an exact form is a differential form, α, that is the exterior derivative of another differential form β. Thus, an exact form is in the image of d, and a closed form is in the kernel of d.

  4. Integrability conditions for differential systems - Wikipedia

    en.wikipedia.org/wiki/Integrability_conditions...

    To elaborate, a Pfaffian system is a set of 1-forms on a smooth manifold (which one sets equal to 0 to find solutions to the system). Given a collection of differential 1-forms , =,, …, on an -dimensional manifold ⁠ ⁠, an integral manifold is an immersed (not necessarily embedded) submanifold whose tangent space at every point is ...

  5. Differential form - Wikipedia

    en.wikipedia.org/wiki/Differential_form

    The exterior derivative is an operation on differential forms that, given a k-form , produces a (k+1)-form . This operation extends the differential of a function (a function can be considered as a 0-form, and its differential is () = ′ ()).

  6. Classification of manifolds - Wikipedia

    en.wikipedia.org/wiki/Classification_of_manifolds

    A topological manifold that is in the image of is said to "admit a differentiable structure", and the fiber over a given topological manifold is "the different differentiable structures on the given topological manifold". Thus given two categories, the two natural questions are:

  7. Spaces of test functions and distributions - Wikipedia

    en.wikipedia.org/wiki/Spaces_of_test_functions...

    The above characterizations can be used to determine whether or not a linear functional is a distribution, but more advanced uses of distributions and test functions (such as applications to differential equations) is limited if no topologies are placed on () and ().

  8. Weak derivative - Wikipedia

    en.wikipedia.org/wiki/Weak_derivative

    Let be a function in the Lebesgue space ([,]).We say that in ([,]) is a weak derivative of if ′ = ()for all infinitely differentiable functions with () = =.. Generalizing to dimensions, if and are in the space () of locally integrable functions for some open set, and if is a multi-index, we say that is the -weak derivative of if

  9. Activation function - Wikipedia

    en.wikipedia.org/wiki/Activation_function

    Continuously differentiable This property is desirable (ReLU is not continuously differentiable and has some issues with gradient-based optimization, but it is still possible) for enabling gradient-based optimization methods. The binary step activation function is not differentiable at 0, and it differentiates to 0 for all other values, so ...