GY-63_MS5611/libraries/DistanceTable

Distancetable

Arduino library to store a symmetrical distance table in less memory.

Description

The DistanceTable library is a class that stores a symmetrical distance table which is typically N x N entries in less memory space. It uses (N x (N-1))/2 ("in a triangle") as an euclidean distance table is symmetrical around its main diagonal. Furthermore as the main diagonal are all zero it does not need to be stored either.

An ATMEL328 (Arduino) can store a 30 x 30 matrix = 900 floats in 1740 bytes, where it typically would take 900 x 4 = 3600 bytes.

Within the 2K RAM of an Arduino one could store normally a 21 x 21 matrix (1764 bytes).

Interface

• DistanceTable(uint8_t size, float value = 0.0) Constructor, allocates memory and sets initial value to all elements.
• ~DistanceTable(); Destructor, frees memory
• void clear() sets all entries to 0.0.
• void setAll(float value) sets all entries to value;
• void set(uint8_t x, uint8_t y, float value ) sets a value for (x,y) and automatically for (y, x)
• float get(uint8_t x, uint8_t y) gets a value from (x,y). If x == y it will return 0.
• float minimum(uint8_t &x, uint8_t &y) Returns minimum and first occurrence in x and y. It does skip x == y pairs as these are 0.
• float maximum(uint8_t &x, uint8_t &y) Returns maximum and first occurrence in x and y. It does skip x == y pairs as these are 0.
• uint16_t count(value, epsilon) counts the number of occurrences of value. As we are comparing floats the epsilon can set a margin for 'almost equal'.

Debug

• void dump(Print * stream = &Serial) dumps distance table , default to serial.
• uint8_t dimension() dimension of the table == parameter in constructor.
• uint16_t elements() amount of elements allocated.
• uint16_t memoryUsed() amount of memory used.

Operational

See examples.

Future

• improve documentation
• clear() could set all to NAN? is that better as it indicates unknown?
  • setAll() let the user decide.
• would DT(x,y) == -DT(y,x) a special case? (for all xy pairs) interesting!!
  • e.g. difference in height?
  • game with transactions between players?
  • it would become a magnitude symmetrical distance table
• countAbove(float value) no epsilon needed
• add examples
  • Note: table can be used for other symmetrical 2D tables.
  • And therefore include negative values.
• derived or related classes
  • int64_t int32_t int16_t int8_t + unsigned variants. (8 variations?)
  • Template class?
• sum of all distances?
• Hamilton paths?
• idea for very sparse matrix? array of struct (x,y,value);