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nan

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nan [Sat Jun 26 22:20:22 2010] Alexander |
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====== Missing Values (NaN) in Tables and Calculations ====== | ====== Missing Values (NaN) in Tables and Calculations ====== | ||

- | In computing, NaN, which stands for Not a Number, is a value or symbol that is usually produced as the result of an operation on invalid input operands. For example, most floating-point units are unable to explicitly calculate the square root of negative numbers, and will instead indicate that the operation was invalid and return a NaN result. | + | In computing, NaN, which stands for Not a Number, is a value or symbol that is usually produced as a result of an operation on invalid input operands. For example, most floating-point units are unable to explicitly calculate the square root of negative numbers, and will instead indicate that the operation was invalid and return a NaN result. |

- | An invalid operation is not the same as an arithmetic overflow (which returns a positive or negative infinity). Arithmetic operations involving NaN always produce NaN, allowing the value to propagate through a calculation so that errors can be detected at the end without extensive testing during intermediate stages. | + | An invalid operation is not the same as an arithmetic overflow (which returns a positive or negative infinity). Arithmetic operations involving NaN always produce NaN, allowing the value to propagate through a calculation so that errors can be detected at the end without extensive testing during intermediate stages. A NaN does not compare equal to any number or NaN. |

- | | + | |

- | A NaN does not compare equal to any number or NaN. You can therefore test whether a variable has a NaN value by comparing it to itself, thus if ''. | + | |

==== How does a NaN appear? ==== | ==== How does a NaN appear? ==== | ||

- | There are three kinds of operation which return NaN: | + | There are three kinds of operations which return NaN: |

- Operations with a NaN as at least one operand, e.g. '' | - Operations with a NaN as at least one operand, e.g. '' | ||

- Indeterminate forms | - Indeterminate forms | ||

- | * The divisions '' | + | * Divisions '' |

- | * The multiplications '' | + | * Multiplications '' |

- | * The power '' | + | * Power '' |

- | * The additions '' | + | * Additions '' |

- Real operations with complex results | - Real operations with complex results | ||

- | * The square root of a negative number | + | * Square root of a negative number |

- | * The logarithm of a negative number | + | * Logarithm of a negative number |

- | * The tangent of an odd multiple of 90 degrees (or //π///2 radians) | + | * Tangent of an odd multiple of 90 degrees (or //π///2 radians) |

- | * The inverse sine or cosine of a number which is less than -1 or greater than +1. | + | * Inverse sine or cosine of a number which is less than -1 or greater than +1. |

=== Examples === | === Examples === | ||

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===== NaN in Expressions ===== | ===== NaN in Expressions ===== | ||

You can use predefined constants '' | You can use predefined constants '' | ||

+ | |||

+ | The '' | ||

=== Example === | === Example === | ||

- | * If you set [[set_column_formula|Column Formula]] ''returns only positive values from column B. Negative values are replaced with NaN value. You can use this expression to filter negative values if you do not want to use them in future calculations. Note that //expression. | + | * If you set a [[set_column_formula|Column Formula]] ''will return only positive values from column B. Negative values are replaced with NaN value. You can use this expression to filter negative values if you do not want to use them in future calculations. Note that //expressions. |

nan.txt · Last modified: Sat Jan 16 20:07:19 2021 by Alexander

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