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  2. Direct method in the calculus of variations - Wikipedia

    en.wikipedia.org/wiki/Direct_method_in_the...

    The direct method may often be applied with success when the space is a subset of a separable reflexive Banach space. In this case the sequential Banach–Alaoglu theorem implies that any bounded sequence ( u n ) {\displaystyle (u_{n})} in V {\displaystyle V} has a subsequence that converges to some u 0 {\displaystyle u_{0}} in W {\displaystyle ...

  3. Calculus of variations - Wikipedia

    en.wikipedia.org/wiki/Calculus_of_Variations

    Calculus of variations is concerned with variations of functionals, which are small changes in the functional's value due to small changes in the function that is its argument. The first variation [l] is defined as the linear part of the change in the functional, and the second variation [m] is defined as the quadratic part. [22]

  4. Fundamental lemma of the calculus of variations - Wikipedia

    en.wikipedia.org/wiki/Fundamental_lemma_of_the...

    In mathematics, specifically in the calculus of variations, a variation δf of a function f can be concentrated on an arbitrarily small interval, but not a single point. Accordingly, the necessary condition of extremum ( functional derivative equal zero) appears in a weak formulation (variational form) integrated with an arbitrary function δf .

  5. Direct comparison test - Wikipedia

    en.wikipedia.org/wiki/Direct_comparison_test

    In mathematics, the comparison test, sometimes called the direct comparison test to distinguish it from similar related tests (especially the limit comparison test), provides a way of deducing whether an infinite series or an improper integral converges or diverges by comparing the series or integral to one whose convergence properties are known.

  6. Direct method (education) - Wikipedia

    en.wikipedia.org/wiki/Direct_method_(education)

    Go back to 1 and 2, mix in 3, practice (X-Y-Z; Z-Y-X; Y-Y-Z, etc.) and continue building up to an appropriate number of Elements (maybe as many as 20 per lesson, depending on the student, see B.1), practising all possible combinations and repeating 5-20 times each combination.

  7. Goldberg Variations - Wikipedia

    en.wikipedia.org/wiki/Goldberg_Variations

    The second of the three minor key variations, variation 21 has a tone that is somber or even tragic, which contrasts starkly with variation 20. [13] The bass line here is one of the most eloquent found in the variations, to which Bach adds chromatic intervals that provide tonal shadings. [13] This variation is a canon at the seventh in 4

  8. Diabelli Variations - Wikipedia

    en.wikipedia.org/wiki/Diabelli_Variations

    While Beethoven's first variation stays close to the melody of Diabelli's theme, there is nothing waltz-like about it. It is a strong, heavily accented march in 4 4 time, greatly differing from the character and 3 4 time of the theme. This sharp break from Diabelli announces that the series will not consist of mere decorative variations on a theme.

  9. Variations on a Theme by Haydn - Wikipedia

    en.wikipedia.org/wiki/Variations_on_a_Theme_by_Haydn

    A detailed survey of the controversy can be found in Douglas Yeo's 2004 edition of the "Haydn" piece (ISMN M-57015-175-1). [3] In 1870, Brahms's friend Carl Ferdinand Pohl, the librarian of the Vienna Philharmonic Society , who was working on a Haydn biography at the time, showed Brahms a transcription he had made of a piece attributed to Haydn ...