What is the meaning of A (1: ,: ) in matlab

What is the meaning of A (1 ,: ,:) in matlab

the matrix A is 4x4

so What is the meaning A (1,: ,:) =4*A (2,: ,:)

and A (4,: ,:) =7*A (2,: ,:)

Answer 1

[Davide Masiello]

If there are three indexes specified, it makes sense only if your matrix has three dimensions.

If it is actually 4x4, then A(1,:,:) yields the same result of A(1,:), i.e. extracting the first row of A.

So, the actual operation you are performing is A(1,:) = 4*A(2,:), which replaces the first row of A with its second row multiplied by 4.

Likewise, A(1,:) = 7*A(2,:) replaces the first row of A with its second row multiplied by 7.

[alize beemiel]

thank you sir

but why we use this anotation or when we can use or not this anotation

i found it almost everywhere

[Davide Masiello]

Any time you need to extract a portion of a matrix you will find that kind of syntax.

For instance, if you write A(1,2) it will extract the element of A that is in the first row and second colum.

In the case of A(1,:) the colon symbol just tells MatLab that you want all the values in row 1.

In my mind I usually read it "the first row and all the columns of A", but that might be personal.

Please let me know if this makes sense, and if yes please consider accepting the answer.

[alize beemiel]

thank you sir

for your help

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