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Python sets are very much like mathematical sets, and support operations like set intersection and union. Python also features a frozenset class for immutable sets, see Collection types. Dictionaries (class dict) are mutable mappings tying keys and corresponding values. Python has special syntax to create dictionaries ({key: value})
While base ten is normally used for scientific notation, powers of other bases can be used too, [25] base 2 being the next most commonly used one. For example, in base-2 scientific notation, the number 1001 b in binary (=9 d) is written as 1.001 b × 2 d 11 b or 1.001 b × 10 b 11 b using binary numbers (or shorter 1.001 × 10 11 if binary ...
To approximate the greater range and precision of real numbers, we have to abandon signed integers and fixed-point numbers and go to a "floating-point" format. In the decimal system, we are familiar with floating-point numbers of the form (scientific notation): 1.1030402 × 10 5 = 1.1030402 × 100000 = 110304.02. or, more compactly: 1.1030402E5
As a power of ten, the scaling factor is then indicated separately at the end of the number. For example, the orbital period of Jupiter's moon Io is 152,853.5047 seconds, a value that would be represented in standard-form scientific notation as 1.528535047 × 10 5 seconds. Floating-point representation is similar in concept to scientific notation.
Scientific notation always has a single nonzero digit to the left of the point: not 60.22 × 10 22, but 6.022 × 10 23. Engineering notation is similar, but with the exponent adjusted to a multiple of three: 602.2 × 10 21. Avoid mixing scientific and engineering notations: A 2.23 × 10 2 m 2 region covered by 234.0 × 10 6 grains of sand.
The design of floating-point format allows various optimisations, resulting from the easy generation of a base-2 logarithm approximation from an integer view of the raw bit pattern. Integer arithmetic and bit-shifting can yield an approximation to reciprocal square root ( fast inverse square root ), commonly required in computer graphics .
The otherwise binary Wang VS machine supported a 64-bit decimal floating-point format in 1977. [2] The Motorola 68881 supported a format with 17 digits of mantissa and 3 of exponent in 1984, with the floating-point support library for the Motorola 68040 processor providing a compatible 96-bit decimal floating-point storage format in 1990. [2]
Thus, a real number, when written out in normalized scientific notation, is as follows: ± d 0 . d 1 d 2 d 3 ⋯ × 10 n {\displaystyle \pm d_{0}.d_{1}d_{2}d_{3}\dots \times 10^{n}} where n is an integer , d 0 , d 1 , d 2 , d 3 , … , {\textstyle d_{0},d_{1},d_{2},d_{3},\ldots ,} are the digits of the number in base 10, and d 0 {\displaystyle ...