not a number

In a computer, not a number (usually abbreviated NaN) indicates that an arithmetical operation has resulted in a value that is not a number understood (or representable) by the computer. Division by zero is one frequent cause of a result being NaN. Asking for the square root of a negative number is another operation that can result in NaN (unless the computer has been programmed to recognize imaginary numbers).

NaN is not a specific value that can be tested for with the usual comparison operators. The programmer is advised to test for NaN with a special function provided by the programming language (such as isNaN(x) in JavaScript.

Generally, computer algebra systems do not report NaN results even if they do display an error message for a given operation.

References

1 David Flanagan, JavaScript the Definitive Guide: The Definitive Guide. New York: O’Reilly (2006): 24

单词	NotANumber
释义	not a number In a computer, not a number (usually abbreviated NaN) indicates that an arithmetical operation has resulted in a value that is not a number understood (or representable) by the computer. Division by zero is one frequent cause of a result being NaN. Asking for the square root of a negative number is another operation that can result in NaN (unless the computer has been programmed to recognize imaginary numbers). NaN is not a specific value that can be tested for with the usual comparison operators. The programmer is advised to test for NaN with a special function provided by the programming language (such as `isNaN(x)` in JavaScript. Generally, computer algebra systems do not report NaN results even if they do display an error message for a given operation. References 1 David Flanagan, JavaScript the Definitive Guide: The Definitive Guide. New York: O’Reilly (2006): 24
随便看	Sikorski’s extension theorem SilvermanToeplitzTheorem Silverman-Toeplitz theorem SilverRatio silver ratio SilverRectangle silver rectangle SimilarityAndAnalogousSystemsDynamicAdjointnessAndTopologicalEquivalence similarity and analogous systems: dynamic adjointness and topological equivalence SimilarityInGeometry similarity in geometry SimilarityOfTriangles similarity of triangles SimilarMatrix similar matrix SimilitudeOfParabolas similitude of parabolas simIsAnEquivalenceRelation SimonDonaldson Simon Donaldson SimonStevin Simon Stevin SimpleAlgebraicSystem simple algebraic system SimpleAndSemisimpleLieAlgebras