why does matlab use 8 bytes to memorize a number like 1 for example

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lou ham 2020-1-3

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评论： Walter Roberson 2020-1-3

采纳的回答： Walter Roberson

hi,

matlab uses 8 bytes to memorize a number like 1 as double as 2 bytes to memorize it as char?

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Answer 1

Walter Roberson 2020-1-3

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By default if you do not tell MATLAB what datatype to use for a number, it uses IEEE 754 Double Precision floating point representation, which is described in more detail at https://en.wikipedia.org/wiki/IEEE_754

When you use char, MATLAB stores the values in UTF-16, which is representation that uses a minimum of two bytes per code point, with a system for indicating that more bytes may be needed. https://en.wikipedia.org/wiki/UTF-16 Code points up to roughly 55295 can be represented in two bytes (and there are another 8192 later ones with direct representation). This includes characters up to 힣 but does not include some alphabets such as Linear B or Phonecian. https://en.wikipedia.org/wiki/Plane_(Unicode)#Supplementary_Multilingual_Plane -- it is enough to hold most living languages.

Character manupulation and storage is a lot easier when you (usually) do not need to worry about the number of bytes needed to represent characters. Single-byte characters would miss out on a lot of commonly used characters -- for example the Greek characters do not start until about code position 913.

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Answer 2

Bhaskar R 2020-1-3

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MATLAB software takes the defualt value storage memory for numeric a value is double precision floationg value that is 64 bit value in range -2^63 to 2^63-1. When you initialize any value by default it take takes 8 bytes of the memory. In single class memory take 4 bytes.If you want convert default double class value to single class you need to convert explicity as single

x = 1;    % by default it is 64 bit(8 byte), double class 
whos x
  Name      Size            Bytes  Class     Attributes
  x         1x1                 8  double  
x = cast(x, 'single') % or x = single(x)    % converted 32 bit(4 byte), single class
whos x
  Name      Size            Bytes  Class     Attributes
  x         1x1                 4  single 

In case of character data type MATALB takes 2 byte of memory for each character

  x = '1';    % x is character data type with 1 character
  whos x
  Name      Size            Bytes  Class    Attributes
  x         1x1                 2  char
  x = '123456789';    % x is character data type with 9 character
  whos x
  Name      Size            Bytes  Class    Attributes
  x         1x9                18  char