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This question concerns equations in the comment statements in the spm_spm.m file. In the documentation of the structure xVI, the field xX.V is listed as an optional non-sphericity matrix. First, is V part of Vi or part of X? Is that comment incorrect? The equationi is Cov(e) = sigma^2*V. Farther down in the comment section, there is a paragraph that starts "In some instances ..." The end of the paragraph reads: W is stored in xX.W and cov(K*W*e) in xX.V. I do not see how the two covariance expressions fit together. Thank you for any information / explanations. Sincerely, Linda Seltzer