[med-svn] [python-mne] 90/353: FIX : fix stupid mistake in averaging cov

[Yaroslav Halchenko]

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yoh pushed a commit to tag 0.4
in repository python-mne.

commit cc76c0886d343b0528dd6631fc8712a4dded5953
Author: Alexandre Gramfort <alexandre.gramfort at inria.fr>
Date:   Tue Feb 28 15:08:26 2012 +0100

    FIX : fix stupid mistake in averaging cov
---
 mne/cov.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mne/cov.py b/mne/cov.py
index 086f50e..f7acbae 100644
--- a/mne/cov.py
+++ b/mne/cov.py
@@ -97,7 +97,9 @@ class Covariance(object):
         """Add Covariance taking into account number of degrees of freedom"""
         _check_covs_algebra(self, cov)
         this_cov = copy.deepcopy(cov)
-        this_cov.data[:] += self.data
+        this_cov.data[:] = ((this_cov.data * this_cov.nfree) + \
+                            (self.data * self.nfree)) / \
+                                (self.nfree + this_cov.nfree)
         this_cov._cov['nfree'] += self._cov['nfree']
         this_cov.nfree = this_cov._cov['nfree']
         return this_cov
@@ -105,7 +107,9 @@ class Covariance(object):
     def __iadd__(self, cov):
         """Add Covariance taking into account number of degrees of freedom"""
         _check_covs_algebra(self, cov)
-        self.data[:] += cov.data
+        self.data[:] = ((self.data * self.nfree) + \
+                            (cov.data * cov.nfree)) / \
+                                (self.nfree + cov.nfree)
         self._cov['nfree'] += cov._cov['nfree']
         self.nfree = cov._cov['nfree']
         return self

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