What is the difference between the statements: A=2; A=(2); A=[2]?

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edvyan
edvyan 2011-9-5
I am a beginner, got a question about it When making an assignment, it usually uses A=2, and it is also understandable that A=[2] as matrix form. But what's the point of A=(2) here that returns the same value? it works when I am trying to change a value to a matrix.
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edvyan
edvyan 2011-9-5
For a created matrix, i.e. A=[1 2 3;4 5 6], if I want to change the element 2 to 8, we normally use A(2)=8 or uncommonly A(2)=[8]. But why A(2)=(8) returns the same answer [1 2 3;8 5 4] rather than an error notice?
Paulo Silva
Paulo Silva 2011-9-5
It depends where the parenthesis are located on the expression, if you put the ( after the variable it means you are going to insert index or indices values, if you put ( after the equal it will be ignored.

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回答（2 个）

Paulo Silva
Paulo Silva 2011-9-5
In MATLAB values like [2] and (2) are the same as 2, for the ( type they mean other things when used after a variable or function.
now for more values
A=[1 2 3] %same as A=1:3
A is now a vector and if you do A(2) you get the second value of the vector A which is 2
Please read this Matrices and Magic Squares
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Oleg Komarov
Oleg Komarov 2011-9-5
The square brackets should cause a small overhead for calling the concatenation.
Teja Muppirala
Teja Muppirala 2011-9-5
When used in loop indices, square brackets will make things very slow:
%% Very fast
tic
x = 0;
for n = 1:1e6
x = x+1;
end
x
toc
%% Very slow
tic
x = 0;
for n = [1:1e6]
x = x+1;
end
x
toc

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Fangjun Jiang
Fangjun Jiang 2011-9-5
To merely answer your question.
A=2 is the same as A=[2], is because 2 is a special case of a matrix with size as 1x1.
A=2 is the same as A=(2), is because 2 can be regarded as a special case of an calculation, for example, it could be A=(4-3)*2
You may want to learn other use of (),{} and [] in MATLAB. Type 'help {' to see a list of symbols and their use.

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