How to create a binary matrix

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snake eyes
snake eyes on 20 Jul 2011
Commented: Walter Roberson on 19 Jul 2017
I want to make matrix whose each element's size will be 1 bit, i.e, it will be a binary matrix.How can I do it?
Thanks in advance.

Answers (5)

Jan
Jan on 20 Jul 2011
There is not BIT type in Matlab. Usually binary arrays are stored as LOGICAL, which are equivalent to UINT8. E.g.:
B = rand(16, 16) > 0.8;
whos('B')
Now you can pack this in blocks of 8 elements to a UINT8 array:
T = 2 .^ (0:7).';
B8 = transpose(reshape(B, 8, []));
BitArray = uint8(B8 * T);

Friedrich
Friedrich on 20 Jul 2011
Hi,
this is not possible in MATLAB and in other languages too like C or C++. In modern computer architectures, a byte is the smallest addressable unit of memory. To pack multiple bits into a byte requires applying extra bit-shift operations. At the compiler level, it's a trade off of memory vs. speed requirements (and in high-performance software, those extra bit-shift operations can add up and slow down the application needlessly).
  3 Comments
Walter Roberson
Walter Roberson on 20 Jul 2011
C does not specify whether bit-fields start from the beginning or the end of a word, and C permits but does not require bit-fields to cross words. In C, arrays of bit-fields are arrays of words: the "packed" attribute possibility was removed from the C language before C was standardized. There is thus no binary matrix in C, just arrays of structs whose members are bit fields.
Walter Roberson
Walter Roberson on 20 Jul 2011
Well, in _popular_ computer architectures; bit-sliced and bit-addressable architectures still have their purposes.

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Sean de Wolski
Sean de Wolski on 20 Jul 2011
To get logical binary values either use:
x = logical(x)
or any conditional operator e.g.
x = x>7
x = x==11;

Image Analyst
Image Analyst on 22 May 2017
Edited: Image Analyst on 22 May 2017
Use true():
t = true(numRows, numColumns);
"whos" will show you it's one byte per element, like the other solutions.
>> t = true(4,5)
t =
4×5 logical array
1 1 1 1 1
1 1 1 1 1
1 1 1 1 1
1 1 1 1 1
>> whos t
Name Size Bytes Class Attributes
t 4x5 20 logical
To get one bit per element, instead of one byte per element, I think you'll have to pack them together yourself.

Ekta Gujral
Ekta Gujral on 19 Jul 2017
A = randi([0 1], n,m)
  1 Comment
Walter Roberson
Walter Roberson on 19 Jul 2017
This produces an array of double, not bits.

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