A(B)=0 What is its meaning?

A=rand(5)

B=A>0.8

A(B)=0

Can you tell me what is A(B)=0 meaning?

Answer 1

[Fangjun Jiang]

B is a logical index matrix. You can see the value is 1 (true) or 0 (false) wherever the corresponding value in A is greater than 0.8.

A(B)=0 means for all those places where B's value is true, set the corresponding value in A to 0.

Use this example to see it better.

A=magic(5)
B=A>10
A(B)=0

[zhenyu zeng]

I knew what is its meaning now. But can you tell me why matlab do this?

[Torsten]

It's the same as if you ask why MATLAB loops if you write

for i=1:n
  ...
end 

It's just MATLAB syntax.

Look up "Logical indexing":

https://blogs.mathworks.com/loren/2013/02/20/logical-indexing-multiple-conditions/

[Fangjun Jiang]

It is a very efficient way for programming.

Answer 2

[Torsten]

All numbers in the matrix A that are bigger than 0.8 are set to 0.