Closed And Exact Differential Forms
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 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.
For an exact form α, α = dβ for some differential form β of one-lesser degree than α. The form β is called a "potential form" or "primitive" for α. Since d2 = 0, β is not unique, but can be modified by the addition of the differential of a two-step-lower-order form.
Because d2 = 0, any exact form is automatically closed. The question of whether every closed form is exact depends on the topology of the domain of interest. On a contractible domain, every closed form is exact by the Poincaré lemma. More general questions of this kind on an arbitrary differentiable manifold are the subject of de Rham cohomology, that allows one to obtain purely topological information using differential methods.
Read more about Closed And Exact Differential Forms: Examples, Examples in Low Dimensions, Poincaré Lemma, Formulation As Cohomology, Application in Electrodynamics
Famous quotes containing the words closed, exact, differential and/or forms:
“For a long time, I went to bed early. Sometimes, my candle barely put out, my eyes closed so quickly that I did not have the time to say to myself: “I am falling asleep”.”
—Marcel Proust (1871–1922)
“His eye had become minutely exact as to the book and its position. Then he resolved that he would not look at the book again, would not turn a glance on it unless it might be when he had made up his mind to reveal its contents.”
—Anthony Trollope (1815–1882)
“But how is one to make a scientist understand that there is something unalterably deranged about differential calculus, quantum theory, or the obscene and so inanely liturgical ordeals of the precession of the equinoxes.”
—Antonin Artaud (1896–1948)
“Literary works cannot be taken over like factories, or literary forms of expression like industrial methods. Realist writing, of which history offers many widely varying examples, is likewise conditioned by the question of how, when and for what class it is made use of.”
—Bertolt Brecht (1898–1956)