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  2. 0.999... - Wikipedia

    en.wikipedia.org/wiki/0.999...

    The standard definition of the number 0.999... is the limit of the sequence 0.9, 0.99, 0.999, ... ‍. A different definition involves an ultralimit, i.e., the equivalence class [(0.9, 0.99, 0.999, ...)] of this sequence in the ultrapower construction, which is a number that falls short of 1 by an infinitesimal amount. [66]

  3. Precision and recall - Wikipedia

    en.wikipedia.org/wiki/Precision_and_recall

    In a classification task, the precision for a class is the number of true positives (i.e. the number of items correctly labelled as belonging to the positive class) divided by the total number of elements labelled as belonging to the positive class (i.e. the sum of true positives and false positives, which are items incorrectly labelled as belonging to the class).

  4. Short interest ratio - Wikipedia

    en.wikipedia.org/wiki/Short_interest_ratio

    The short interest ratio (also called days-to-cover ratio) [1] represents the number of days it takes short sellers on average to cover their positions, that is repurchase all of the borrowed shares. It is calculated by dividing the number of shares sold short by the average daily trading volume, generally over the last 30 trading days.

  5. Receiver operating characteristic - Wikipedia

    en.wikipedia.org/wiki/Receiver_operating...

    A classification model (classifier or diagnosis [7]) is a mapping of instances between certain classes/groups.Because the classifier or diagnosis result can be an arbitrary real value (continuous output), the classifier boundary between classes must be determined by a threshold value (for instance, to determine whether a person has hypertension based on a blood pressure measure).

  6. Branching fraction - Wikipedia

    en.wikipedia.org/wiki/Branching_fraction

    In some instances, instead of a branching fraction, a branching ratio is used. In this case, the branching ratio is just the ratio of the branching fractions between two states. To use our example from before, if the branching fraction to state |g is ⁠ p {\displaystyle p} ⁠ , then the branching ratio comparing the transition rates to |g and ...

  7. Chemistry - Wikipedia

    en.wikipedia.org/wiki/Chemistry

    Chemistry is the scientific study of the properties and behavior of matter. [1] It is a physical science within the natural sciences that studies the chemical elements that make up matter and compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during reactions with other substances.

  8. Water - Wikipedia

    en.wikipedia.org/wiki/Water

    Water is an inorganic compound with the chemical formula H 2 O.It is a transparent, tasteless, odorless, [c] and nearly colorless chemical substance.It is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent [20]).