If you want to format your data output as an XML file, here's how to do it without doing any complicated string handling. MATLAB can use the XML handling capabilities of Java very easily. Here's how:

Assume that your data is available in arrays arrData1 and arrData2. Create an XML document node, say Node1 as follows:

docNode = com.mathworks.xml.XMLUtils.createDocument('Node1');
docRootNode = docNode.getDocumentElement;

Now put the data in the data nodes..

for i=1:length(arrData1),
% create nodes..
    elPar = docNode.createElement('DataParent');
    elData1 = docNode.createElement('Data1');
    elData2 = docNode.createElement('Data2');

% put data in nodes..
    elData1.appendChild(...
    docNode.createTextNode(sprintf('%f', arrData1(i))));
    elData2.appendChild(...
    docNode.createTextNode(sprintf('%f', arrData2(i))));

% put nodes in the correct positions..
    elParent.appendChild(elData1);
    elParent.appendChild(elData2);
    docRootNode.appendChild(elParent);
end

Now save the XML document. You can save it directly, or use uiputfile to get the standard save dialog of the OS.

[filename, pathname] = uiputfile(...
sprintf('%s.xml', datFile), 'Save XML file as');

% Save the XML document.
% xmlFileName = [dataOutFile,'.xml'];
    xmlFileName = fullfile(pathname, filename);
    xmlwrite(xmlFileName,docNode);
% open xml file to see your output
    edit(xmlFileName);

To see more ways of using XML with MATLAB, refer to Java's documentation and play around to see what works.

I have one doubt here: what is the size limit to create a xml function this way.
I tried to use this technique, storing the value of 25 vectors (it would create a type of matrix 9x25), but its not working. I think its because of the method to do it, "<?xml version="1.0" encoding="utf-8"?>", but there's a way to do it differently?

Pls, any help?