extracting nonpivot columns from a matrix

Hi, I have a function nonpuvotcols that takes a matrix as input and produces a matrix consisting of the nonpivot columns. For the last step of my code, I need to extract all the nonpivot colums from the input matrix, but I think I'm only extracting the last nonpivot column from the matrix.

%  Returns the nonpivot columns from the matrix A
function npc = nonpivotcols(A)

% determine n the number of columns of A 
[m, n_plus_one] = size(A)
n = n_plus_one-1 

% use rref to obtain a list of the pivot columns of A (pcols)
[R pcols]=rref(A);
A(:,pcols)=[];
% from the list of all columns 1:n remove pcols to obtain a list of the nonpivot columns (fcols)
 
%% Getting columns which if fcol
[r,fcols]=size(A); 

%(HELP) extract the nonpivot columns from A
npc = A(:,fcols);           
end

This is my code. Please help me for the last commented part, which is to extract all the nonpivot columns.

A = [ 1 1 2 2 3 3; 4 4 5 5 6 6; 7 7 8 8 9 9]     
[R, pcols] = rref(A)
nonpivotcols(A)

And here is the code to call the function.

Thank you!

Answer 1

[dpb]

function npc = nonpivotcols(A)

  [~,p]=rref(A);
  A(:,pcols)=[];
  npc=A;
end

or

function npc = nonpivotcols(A)

  [~,p]=rref(A);
  npc=A(:,setdiff(1:size(A,2),p));
end