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  2. Vertical line test - Wikipedia

    en.wikipedia.org/wiki/Vertical_line_test

    A function can only have one output, y, for each unique input, x. If a vertical line intersects a curve on an xy-plane more than once then for one value of x the curve has more than one value of y, and so, the curve does not represent a function. If all vertical lines intersect a curve at most once then the curve represents a function. [1]

  3. Parity-check matrix - Wikipedia

    en.wikipedia.org/wiki/Parity-check_matrix

    Formally, a parity check matrix H of a linear code C is a generator matrix of the dual code, C ⊥. This means that a codeword c is in C if and only if the matrix-vector product Hc ⊤ = 0 (some authors [1] would write this in an equivalent form, cH ⊤ = 0.) The rows of a parity check matrix are the coefficients of the parity check equations. [2]

  4. Line graph - Wikipedia

    en.wikipedia.org/wiki/Line_graph

    In the mathematical discipline of graph theory, the line graph of an undirected graph G is another graph L(G) that represents the adjacencies between edges of G. L(G) is constructed in the following way: for each edge in G, make a vertex in L(G); for every two edges in G that have a vertex in common, make an edge between their corresponding vertices in L(G).

  5. Data analysis - Wikipedia

    en.wikipedia.org/wiki/Data_analysis

    This is an attempt to model or fit an equation line or curve to the data, such that Y is a function of X. [74] [75] Necessary condition analysis (NCA) may be used when the analyst is trying to determine the extent to which independent variable X allows variable Y (e.g., "To what extent is a certain unemployment rate (X) necessary for a certain ...

  6. Relational algebra - Wikipedia

    en.wikipedia.org/wiki/Relational_algebra

    The relational algebra uses set union, set difference, and Cartesian product from set theory, and adds additional constraints to these operators to create new ones.. For set union and set difference, the two relations involved must be union-compatible—that is, the two relations must have the same set of attributes.

  7. Incidence matrix - Wikipedia

    en.wikipedia.org/wiki/Incidence_matrix

    The column of a positive edge has a 1 in the row corresponding to one endpoint and a −1 in the row corresponding to the other endpoint, just like an edge in an ordinary (unsigned) graph. The column of a negative edge has either a 1 or a −1 in both rows. The line graph and Kirchhoff matrix properties generalize to signed graphs.

  8. Look-ahead (backtracking) - Wikipedia

    en.wikipedia.org/wiki/Look-ahead_(backtracking)

    Forward checking only checks whether each of the unassigned variables x 3 and x 4 is consistent with the partial assignment, removing the value 2 from their domains. The simpler technique for evaluating the effect of a specific assignment to a variable is called forward checking . [ 1 ]

  9. Surrogate key - Wikipedia

    en.wikipedia.org/wiki/Surrogate_key

    Having the key independent of all other columns insulates the database relationships from changes in data values or database design [5] (making the database more agile) and guarantees uniqueness. In a temporal database, it is necessary to distinguish between the surrogate key and the business key. Every row would have both a business key and a ...