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In mathematics, especially vector calculusand differential topology, a closed formis a differential formαwhose exterior derivativeis zero (dα= 0), and an exact formis a differential form, α, that is the exterior derivative of another differential form β. Thus, an exactform is in the imageof d, and a closedform is in the kernelof d.
Identifying first order exact differential equations. Let the functions , , , and , where the subscripts denote the partial derivative with respect to the relative variable, be continuous in the region . Then the differential equation. is exact if and only if. That is, there exists a function , called a potential function, such that.
In computational complexity theory, Karp's 21 NP-complete problems are a set of computational problems which are NP-complete.In his 1972 paper, "Reducibility Among Combinatorial Problems", [1] Richard Karp used Stephen Cook's 1971 theorem that the boolean satisfiability problem is NP-complete [2] (also called the Cook-Levin theorem) to show that there is a polynomial time many-one reduction ...
Problems 1, 2, 5, 6, [g] 9, 11, 12, 15, 21, and 22 have solutions that have partial acceptance, but there exists some controversy as to whether they resolve the problems. That leaves 8 (the Riemann hypothesis), 13 and 16 [h] unresolved, and 4 and 23 as too vague to ever be described as solved. The withdrawn 24 would also be in this class.
The problem for graphs is NP-complete if the edge lengths are assumed integers. The problem for points on the plane is NP-complete with the discretized Euclidean metric and rectilinear metric. The problem is known to be NP-hard with the (non-discretized) Euclidean metric. [ 3]: ND22, ND23. Vehicle routing problem.
163 million (2017) [ 8] Major depressive disorder ( MDD ), also known as clinical depression, is a mental disorder [ 9] characterized by at least two weeks of pervasive low mood, low self-esteem, and loss of interest or pleasure in normally enjoyable activities. Introduced by a group of US clinicians in the mid-1970s, [ 10] the term was adopted ...
In the guillotine cutting problem, both the items and the "bins" are two-dimensional rectangles rather than one-dimensional numbers, and the items have to be cut from the bin using end-to-end cuts. In the selfish bin packing problem, each item is a player who wants to minimize its cost. [53]
More formally, given a universe and a family of subsets of , a set cover is a subfamily of sets whose union is . In the set cover decision problem, the input is a pair and an integer ; the question is whether there is a set cover of size or less. In the set cover optimization problem, the input is a pair , and the task is to find a set cover ...