<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Dear Thomas,<div><br></div><div>if your data is 64 electrodes + reference, you should never get rank 65 even after your re-introduce the reference channel CPz. The sum of all of your channel at each time point should be 0 under the average reference assumption which is used to re-introduce your reference channel. The fact that you are getting a rank of 65 when you do</div><div><br></div><div style="font-size: 16px; ">rank(EEG.data(:,:,1))</div><div><br></div><div>is puzzling though.</div><div>Best,</div><div><br></div><div>Arno</div><div><br><div><div>On Jun 22, 2011, at 12:12 PM, Thomas Schüller wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">
<div bgcolor="#ffffff" text="#000000">
<div class="moz-text-html" lang="x-western"> <font color="#000000">Hi
eeglab list gurus<br>
<br>
I have a problem that I really can't figure out on my own. I
have eeg data recorded from 64 electrodes + reference</font> <font class="Apple-style-span"> (CPz). I find that
using different filters changes the rank of the matrix in ways I
would not have anticipated.</font><font color="#000000"><br>
<br>
First, I used a Butterworth highpass (.5Hz) and a Chebychew
lowpass (25Hz) filter </font> <font class="Apple-style-span">on the raw data and then </font><font color="#000000">reconstructed CPz </font><font class="Apple-style-span">in the process of</font><font color="#000000"> re-referenc</font><font class="Apple-style-span">ing</font><font color="#000000"> to average</font><font class="Apple-style-span">, and then </font><font color="#000000">epoched</font><font class="Apple-style-span"> the file</font><font color="#000000"> resulting in a EEG.data(:,:,1) matrix with rank
65.<br>
When computing the ICA using runica() I get a warning: "fixing
rank computation inconsitency (65 vs 64) most likely because
running under Linux 64-bit Matlab".<br>
The server that I ran it on is indeed 64-bit, but it's a windows
server... the ICA creates 65 ICs, as </font><font class="Apple-style-span">many </font><font color="#000000">as there are Channels!<br>
<br>
Second, I used the eegfilt function (highpass: .5 / lowpass:25)
on the raw data and repeated the process as described above.
Now, after reconstructing and re-referencing EEG.data(:,:,1) has
a rank of 64.</font> <font color="#000000"><br>
When computing ICA i get the warning: "Data rank (64) is smaller
than the number of channels (65)"<br>
and sure enough ICA composes only 64 ICs!<br>
<br>
Does any one know why this is happening?</font> <font color="#000000"><br>
<br>
Many thanks!</font> <font color="#000000"><br>
</font><font color="#000000"> <br>
Thomas</font> </div>
</div>
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