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	UnitsOfQuadraticFields units of quadratic fields UnitsOfRealCubicFieldsWithExactlyOneRealEmbedding units of real cubic fields with exactly one real embedding UnitTriangularMatrix unit triangular matrix UnitVector unit vector Unit Vectors in Curvilinear Coordinates UnitVectorsInCurvilinearCoordinates1 Unity unity UnityOfSubring unity of subring UnityPlusNilpotentIsUnit unity plus nilpotent is unit Univalence implies function extensionality UnivalentAnalyticFunction univalent analytic function UnivalentFoundations Univalent foundations UniversalAssumption universal assumption UniversalBundle universal bundle