How to read a triangular matrix
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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.
2 个评论
Guillaume
2018-4-20
To avoid ambiguity it would be better if you attached an example text file.
Peter Kerekes
2018-4-20
回答（2 个）
Walter Roberson
2018-4-20
0 个投票
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()
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)
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2018-4-20
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