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As a simple first test, I trained an HMatrix using the first three values of the shape vector on electron clusters and calculated chi^2 values using the same electron data and pion data (see attached files SimpleHMatrixBuilder.java and SimpleHMatrixTester.java). The histograms of these chi^2 values are below.
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The electrons exhibit a very tightly constrained response, whereas the majority of the pions have a very high chi^2 value. There is a peak at 1 in the pion data, but it is one tenth the height of the electron peak. This is most likely due to pion showers which deposit a significant portion of their energy in the EM calorimeter and are discontinuous.