Abscissa and ordinate a parametric equation. Used in this way, the abscissa can be thought of as a coordinate-geometry analog to the independent variable in a mathematical model or experiment (with any ordinates filling a role analogous to dependent variables). Abscissa and ordinate In mathematics, the abscissa (; plural "abscissae" or "abscissæ" or "abscissas") and the ordinate are respectively the first and second coordinate of a point in a coordinate system. The abscissa of a point is the signed measure of its projection on the primary axis, whose absolute value is the distance between the projection and the origin of the axis, and
Topological graph embeddings of graphs in surfaces (that is, drawings without crossings). A fundamental problem in extremal graph theory is the following: what is the maximum number of edges that a graph of "n" vertices can have if it contains no subgraph belonging to a given class of "forbidden subgraphs"? The prototype of such results is Turán's theorem, where there is one forbidden subgraph: a complete graph with "k" vertices ("k" is fixed). Analogous questions can be raised for topological and geometric graphs, with the difference that now certain "geometric subconfigurations" are forbidden. Historically, the first instance of such a theorem is