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128 lines
5.9 KiB
Markdown
128 lines
5.9 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/statHelpers/blob/master/LICENSE)
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[](https://github.com/RobTillaart/statHelpers/releases)
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# statHelpers
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Arduino library with a number of statistic helper functions.
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## Description
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This library contains functions that have the goal to help with
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some basic statistical calculations.
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## Functions
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### Permutation
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returns how many different ways one can choose a set of k elements
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from a set of n. The order does matter.
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The limits mentioned is the n for which all k still work.
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- **uint32_t permutations(n, k)** exact up to 12
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- **uint64_t permutations64(n, k)** exact up to 20
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- **double dpermutations(n, k)** not exact up to 34 (4 byte) or 170 (8 byte)
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If you need a larger n but k is near 0 the functions will still work, but
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to which k differs per value for n. (no formula found, and an overflow
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detection takes overhead).
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- **nextPermutation<Type>(array, size)** given an array of type T it finds the next permutation
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of that array in a lexicographical way. ABCD --> ABDC.
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Based upon // http://www.nayuki.io/page/next-lexicographical-permutation-algorithm although
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other same code examples exist.
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### Factorial
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- **uint32_t factorial(n)** exact up to 12!
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- **uint64_t factorial64(n)** exact up to 20! (Print 64 bit ints with my printHelpers)
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- **double dfactorial(n)** not exact up to 34! (4 byte) or 170! (8 byte)
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- **double stirling(n)** approximation function for factorial (right magnitude)
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**dfactorial()** is quite accurate over the whole range.
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**stirling()** is up to 3x faster for large n (> 100),
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but accuracy is less than the **dfactorial()**, see example.
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### SemiFactorial
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- **uint32_t semiFactorial(n)** exact up to 20!!
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- **uint64_t semiFactorial64(n)** exact up to 33!! (Print 64 bit integers with my printHelpers)
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- **double dSemiFactorial(n)** not exact up to 56!! (4 byte) or 300!! (8 byte)
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SemiFactorial are defined for
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- **odd** values: n x (n-2) x (n-4) ... x 1
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- **even** values: n x (n-2) x (n-4) ... x 2
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Notes:
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```n! = n!! x (n-1)!!``` this formula allows to calculate the value of n! indirectly
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### Combinations
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returns how many different ways one can choose a set of k elements
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from a set of n. The order does not matter.
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The number of combinations grows fast so n is limited per function.
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The limits mentioned is the n for which all k still work.
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- **uint32_t combinations(n, k)** n = 0 .. 30 (iterative version)
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- **uint64_t combinations64(n, k)** n = 0 .. 61 (iterative version)
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- **uint32_t rcombinations(n, k)** n = 0 .. 30 (recursive version, slightly slower)
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- **uint64_t rcombinations64(n, k)** n = 0 .. 61 (recursive version, slightly slower)
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- **double dcombinations(n, k)** n = 0 .. 125 (4bit) n = 0 .. 1020 (8 bit)
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If you need a larger n but k is near 0 or near n the functions will still work,
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but for which k differs per value for n. (no formula found, and an overflow
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detection takes overhead).
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- **combPascal(n, k)** n = 0 .. 30 but due to double recursion per iteration it takes
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time and a lot of it for larger values. Added for recreational purposes, limited tested.
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## Notes
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- **perm1** is a sketch in the examples that shows a recursive permutation
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algorithm. It generates all permutations of a given char string.
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It allows you to process every instance.
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It is added to this library as it fits in the context.
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### Experimental - large numbers
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- **void bigFactorial(uint32_t n, double &mantissa, uint32_t &exponent)** returns a double mantissa between 0 and 10, and an integer exponent.
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- **void bigPermutation(uint32_t n, uint32_t k, double &mantissa, uint32_t &exponent)** returns a double mantissa between 0 and 10, and an integer exponent.
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- **void bigCombination(uint32_t n, uint32_t k, double &mantissa, uint32_t &exponent)** returns a double mantissa between 0 and 10, and an integer exponent.
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An experimental **bigFactorial(n)** calculation to get an idea of the big numbers. it can calculate factorials up to an exponent of 4294967295 max. 100.000.000! can be done in 38 minutes on an ESP32 @240 Mhz. Maximum value for n is **518678059! == 2.1718890e4294967292** a number that took ~10 hrs to calculate.
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An experimental **bigPermutation(n, k)** calculation, to handle big numbers too. Maximum value for n is **518678059** to have full range support. For small(er) values of k, n can even be much larger, but not larger than 4294967295 max.
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An experimental **bigCombination(n, k)** calculation for big numbers. Not investigated what its maximum value is, but it should be higher than **518678059** as the number of combinations is always smaller than number of permutations.
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#### Experimental - not investigated yet
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To have support for huge numbers one could upgrade the code to use uint64_t as parameter and internally but calculating these values could take a lot of time, although **bigPermutations64(n, k)** and **bigCombinations64(n, k)** would work fast for small values of k.
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- **void bigFactorial64(uint64_t n, double &mantissa, uint64_t &exponent)** returns a double mantissa between 0 and 10, and an integer exponent.
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- **void bigPermutation64(uint64_t n, uint64_t k, double &mantissa, uint64_t &exponent)** returns a double mantissa between 0 and 10, and an integer exponent.
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- **void bigCombination64(uint64_t n, uint64_t k, double &mantissa, uint64_t &exponent)** returns a double mantissa between 0 and 10, and an integer exponent.
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## Future
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- code & example for get Nth Permutation
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- investigate valid range detection for a given (n, k) for combinations and permutations.
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- investigate a bigFloat class to do math for permutations and combinations to substantially larger values.
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## Operation
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See examples
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