How to read a triangular matrix

Hello ! I would like to read an upper triangular(symmetrical) matrix from a txt the format is the forwarding:

A=[1 1 1;
  ' '  1 1;
  ' ' ' ' 1;];

The upper triangle element are missing(' ' is a space character instead) in the txt.

[Guillaume]

To avoid ambiguity it would be better if you attached an example text file.

[Peter Kerekes]

I only have a very big txt, but I can atteche it. It is an 1000x1000 matrix

Answer 1

[Walter Roberson]

Read the values as a single vector. Delete the entries corresponding to the 0 diagonal (I did not look through the entire file to be sure the diagonal is all 0 though.) Noe you should be able to use squareform() to create the full array.

squareform() is mostly used with pdist()

Answer 2

[Guillaume]

fid = fopen('Stext2.txt');
entries = textscan(fid, '%f');   %read every number as one vector
fclose(fid);
msize = (sqrt(8*numel(entries{1})+1)-1)/2;  %size of full matrix
fullmat = zeros(msize);         
fullmat(tril(true(size(fullmat)))) = entries{1};  %fill up lower triangle (since matlab fills columns not rows)
fullmat = fullmat + triu(fullmat.', 1);  %add upper triangle (without main diagonal)