Error message 'Unable to perform assignment because brace indexing is not supported for variables of this type'

I have a code to extract a parameter from a list of file names in a for loop. However, if I run this I get the error message in the title. Where have I gone wrong?

Rarray = zeros(1,19);
cf=0.71;
for file = 1:numel(files')
  myfilename = sprintf('20181030u%d.mat',file)
  matfile{file} = importdata(myfilename);
  A4 = cf*A+B+cf*C;
  B4 = cf*C+D+cf*E;
  C4 = cf*E+F+cf*G;
  D4 = cf*G+H+cf*A;
  V = 2*complex(A4-C4,B4-D4)./(A4+B4+C4+D4);
  for m=1:numel(files')
      R = sum(abs(V))/length(V);
      Rarray(m) = R;
  end
end

[madhan ravi]

upload two sample files two rectify the error

[JJH]

I've uploaded 2 files, they each contain multiple outputs, including A, B, C etc that I use in the code.