Why the matrix is changing from 10X10 to 1X100

My question details in steps 1. generate 10X10 matrix, ones(10) 2. randomly select a site and change it to -1 3. repeat till all the 1 changes to -1 in the matrix. Thanks

clc
clear all
clearvars
format compact

nrows = 10                    
fm_layer = ones(nrows)
E_A = sum(sum(fm_layer))
n = numel(fm_layer);
for k=1:n
  A(k) = -1
  E_B = sum(sum(fm_layer))    
end

[Adam]

If A started out as 10x10 then it should stay as such with that code, but you don't define A any time before your loop so naturally it will just get created and grow into a vector of 100 values in that code.

It is not at all obvious what you are trying to do though. None of your arrays seem to be connected to each other in that code.

[Guillaume]

Adam's comment is very relevant (and answer the question in your title) and your flippant comment is not.

The code as you've posted does not make sense and doesn't seem to even make an attempt at doing what you describe in your question. So we don't even know what it is you're actually asking.

For reference, the code you posted does exactly the same as:

fm_layer = ones(10, 10);
EA = sum(fm_layer(:));
A = ones(1, numel(fm_layer));
EB = EA;  %it does that 100 times

We have no idea what was the purpose of the loop, since it doesn't do much.

[Offroad Jeep]

My question details in steps 1. generate 10X10 matrix, ones(10) 2. randomly select a site and change it to -1 3. repeat till all the 1 change to -1 in the matrix.

Hope now the logic is clear.......

[Guillaume]

If that's what you want, then I believe my answer does it.

[Offroad Jeep]

Thanks ..... I did it ....

Answer 1

[Alexandra Harkai]

Seems like a new array A is created and gets expanded at every iteration. Since the 'numel' of your matrix is 100 (=10*10), it loops through and creates an array of length 100, expanding it element-by-element.

Answer 2

[Guillaume]

If you want to replace the elements of fm_layer one by one in some random order then:

fm_layer = ones(nrows);
for idx = randperm(numel(fm_layer))
   fm_layer(idx) = -1;
   %do something with modifier fm_layer for this step
end