How i select a part or section of a matrix ?

So I want to compare the matlab function inv(A) (to have a matrix inverse of A) with the way we suppose to do at hand the function is : >>> rref([A eye(size(A))]) So example : I got a something like (but freaking bigger (9*18))

* [ 1 0 a b                               [a b
*   0 1 c d ] and I just want to keep the  c d]

[1, 0, a, b; 0, 1, c, d] >>> [a, b; c, d]

How I supposed to do It look like it super simple but now I got no idea how to do. Thank

Answer 1

[Image Analyst]

out = m(:,3:4); % Extract columns 3 and 4 only into a new 2D array.

[Sokratis Panagiotidis]

Hey, how would you select a certain area of a matrix that is not a full column?

I have a 1024x1024 matrix and want to reduced the depicted area into 800x800. I'd be thankful for an answer.

EDIT: Nevermind I managed to do that.

The solution is that with out = m(selected x-area, selected y-area) but I had not understood what the entires exactly meant. So with

out = m(112:912, 112:912);

I managed to create a new matrix or 2D array if you wanna call it like that, and thus projected the area I wanted into it.

Hopefully someone else will get help by it.

[Image Analyst]

@Sokratis Panagiotidis, there are functions to hand-draw ROI shapes like drawrectangle(), drawfreehand(), etc. Or you can just use indexing like you did if you know the row and column locations in advance.

[Muhammad Taha Manzoor]

Hello Image Analyst,

I have a big matrix of some solar flux measurements. I am able to plot the flux map using imagesec but my I am intrested in the flux values which fall in 50 mm dia of circle. I can create a circluar ROI on the image but how do I extract the data within that circle? I mean I have the data stroed in a matrix I just need to crop out the relavent values in the 50 mm dia and then take an avergae of those values

[Image Analyst]

@Muhammad Taha Manzoor make your binary image mask of the circle, like with poly2mask or however, then do

meanIntensity = mean(fluxImage(mask))