"How can I ... a) saves a matrix(i) on each iterration as a value in the workplace"
What I think you mean is to store each iteration of "A". Correct me if that's incorrect. The variable "A" is already stored in the workspace but you're overwriting it upon each iteration of the i-loop.
Below are 2 options.
Option 1: store each matrix in a cell array
% Create a cell array that will store your matrices
Amat = cell(size(files));
for i = 1:N
A=importfile(files(i).name);
Amat{i} = A{:,:}; % <---- store the matrix in the cell array
end
Option 2: if the matrices are all the same size, store them in a 3D array
Amat = nan(m,n,numel(files)); %where m and n are the expected dimension of the matrix
for i = 1:N
A=importfile(files(i).name);
Amat(:,:,i) = A{:,:}; % <---- store the matrix in a 3D array
end
"How can I... b) calculates the by element mean of all these matrices in a new matrix"
If you want the element-wise mean of each matrix (assuming they are all the same size),
% IF YOU CHOSE OPTION 1 ABOVE
% Assumes Amat has 1 row and f columns
[m,n] = size(Amat{1});
f = numel(Amat);
AmatMean = mean(reshape(cell2mat(Amat'),m,n,f),3);
% IF YOU CHOSE OPTION 2 ABOVE
AmatMean = mean(Amat,3);
