What does this means?

Question

Jose99 2023-3-19

编辑： Stephen23 2023-3-19

i was working on a class assignment and then i found this one operation i found it confussing.

G= [ 1  2 3; 4 5 6; 7 8 9];
H=  G([1 3], [1 2]);

what does the function H do to the G matrix?

i tried to change the numbers inside the brackets but it shuffles the elements of the matrix G and i dont understand how it works.

is there any documentation referring to this problem?

Stephen23 2023-3-19

编辑：Stephen23 2023-3-19

"what does the function H do to the G matrix?"

Nothing: there is no function H, and that indexing does not change G at all.

H is simply the name of a variable that the result of some indexing is assigned to, i.e. H is an array.

"is there any documentation referring to this problem?"

Of course, see the end of the section Indexing Matrices with Two Subscripts here:

Indexing is a MATLAB superpower. Basic indexing concepts are introduced here:

Answer 1

Star Strider 2023-3-19

It returns the elements in from rows 1 and 3 in columns 1 and 2 —

G= [ 1  2 3; 4 5 6; 7 8 9];
H=  G([1 3], [1 2])
H = 2×2
     1     2
     7     8

.