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78 lines
3.4 KiB
Markdown
78 lines
3.4 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/DistanceTable/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/DistanceTable/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/Distancetable/blob/master/LICENSE)
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[](https://github.com/RobTillaart/Distancetable/releases)
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# Distancetable
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Arduino library to store a symmetrical distance table in less memory.
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## Description
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The DistanceTable library is a class that stores a symmetrical distance table
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which is typically N x N entries in less memory space.
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It uses (N x (N-1))/2 ("in a triangle") as an euclidean distance table is
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symmetrical around its main diagonal.
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Furthermore as the main diagonal are all zero it does not need to be stored either.
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An ATMEL328 (Arduino) can store a 30 x 30 matrix = 900 floats in 1740 bytes,
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where it typically would take 900 x 4 = 3600 bytes.
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Within the 2K RAM of an Arduino one could store normally a 21 x 21 matrix (1764 bytes).
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## Interface
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- **DistanceTable(uint8_t size, float value = 0.0)** Constructor, allocates memory and
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sets initial value to all elements.
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- **~DistanceTable();** Destructor, frees memory
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- **void clear()** sets all entries to 0.0.
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- **void setAll(float value)** sets all entries to value;
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- **void set(uint8_t x, uint8_t y, float value )** sets a value for (x,y) and automatically for (y, x)
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- **float get(uint8_t x, uint8_t y)** gets a value from (x,y). If x == y it will return 0.
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- **float minimum(uint8_t &x, uint8_t &y)** Returns minimum and first occurrence in x and y.
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It does skip x == y pairs as these are 0.
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- **float maximum(uint8_t &x, uint8_t &y)** Returns maximum and first occurrence in x and y.
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It does skip x == y pairs as these are 0.
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- **uint16_t count(value, epsilon)** counts the number of occurrences of value.
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As we are comparing floats the epsilon can set a margin for 'almost equal'.
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### Debug
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- **void dump(Print \* stream = &Serial)** dumps distance table , default to serial.
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- **uint8_t dimension()** dimension of the table == parameter in constructor.
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- **uint16_t elements()** amount of elements allocated.
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- **uint16_t memoryUsed()** amount of memory used.
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## Operational
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See examples.
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## Future
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- improve documentation
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- **clear()** could set all to NAN? is that better as it indicates unknown?
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- setAll() let the user decide.
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- would DT(x,y) == -DT(y,x) a special case? (for all xy pairs) interesting!!
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- e.g. difference in height?
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- game with transactions between players?
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- it would become a magnitude symmetrical distance table
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- **countAbove(float value)** no epsilon needed
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- add examples
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- Note: table can be used for other symmetrical 2D tables.
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- And therefore include negative values.
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- derived or related classes
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- int64_t int32_t int16_t int8_t + unsigned variants. (8 variations?)
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- Template class?
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- sum of all distances?
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- Hamilton paths?
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- idea for very sparse matrix? array of struct (x,y,value);
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