about dlmwrite

I have a text file which consists of numbers (for example myfile.txt=[1 2 3;4 5 6; 7 8 9]. I want to replace its "5 6 8 9" elements with new matrix (for example A=[3 2;4 1]). Other elements in myfile.text must be same. I tried it with dlmwrite, dlmwrite ('myfile.txt',A,' ',1,2), but other elements was deleted. How can I change only these elements without deleting other elements?

Answer 1

[Fangjun Jiang]

DLMWRITE('FILENAME',M,'DLM',R,C) writes matrix M starting at offset row R, and offset column C in the file. But it will completely over-write the existing file anyway. It just leaves some delimiter to make the offset. It's not going to open the old file, find the offset and just over-write the new data.

You'll have to read in the whole data, do the proper replacement in MATLAB and then write it back.