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The coherence index was defined [http://en.wikipedia.org/w/index.php?title=Structure_tensor&oldid=368781876 in this version of the article] as 0 when the two eigenvalues were zero, that is, when the gradient was uniformly zero within the window. However, the formula for the general case does not have a definite limit when λ<sub>1</sub> and λ<sub>2</sub> both tend to 0, so any definition is equally wrong. Essentially, such a region can be regarded as totally isotropic or totally coherent, or anything in between, depending on what value one chooses to assign to 0/0.<br/> That article also stated that "[the coherence index] is capable of distinguishing between the isotropic and uniform cases." However, when λ<sub>1</sub> = λ<sub>2</sub> > 0, the first case of the definition yields 0, the same as the second case.<br/>pending clarification, I have removed this claim and merely noted that "some authors" define the index as 0 in the uniform case.<br/>--[[User:Jorge Stolfi|Jorge Stolfi]] ([[User talk:Jorge Stolfi|talk]]) 06:40, 20 August 2010 (UTC)
== Name "Second moment matrix" ambigous/improper? ==
How standard is the name "second moment matrix"? I ask because the name is used in other areas, such as statistics and mechanics, but the meaning does not seem to be the same. Or is it? --[[User:Jorge Stolfi|Jorge Stolfi]] ([[User talk:Jorge Stolfi|talk]]) 00:19, 21 August 2010 (UTC)
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