function kch_convar(varargin)

% Examines a design matrix (specified in SPMcfg and returns 
% various details - such as variance of contrasts, optimal 
% low-pass filter (the high-pass cutoff period, etc).
% ------------------------------------
% Based on some email correspondence with Eric Zarahn, from Mar 1999
% where he outlined the following idea:
%
% SPM uses low-frequency confounds to model and remove low-frequency
% noise. Low-frequency confounds will model this noise, and eliminate
% the effects in the estimation of noise. However, there is something
% to take into account and that is the possible presence of low-
% frequencies in the comparisons (or contrasts) used at the statistical
% inference stage. Substantial overlap of the low-frequency confounds
% and the comparisons in frequency space will reduce the sensitivity
% to perhaps unacceptable levels. This will result in an increase in 
% the variance of the comparison. So, as a measure of how much a 
% contrasts overlaps with the low-frequency confounds, one can examine
% the contrasts' variance at a given hi-pass cutoff relative to using 
% no confounds. 
%
% A comparison (or contrast) in this context is some linear combination
% of parameter estimates. It can be specified by a vector where the
% elements of the vector specify the weights on the paramter estimates.
% The variance of a contrast depends on the variances and covariances 
% of the parameter estimates given non-zero weights. These variances and
% covariances in turn depend in a somewhat complex way on all the 
% covariates in the model. 
%
%
			 
% ==========================================================
% Kalina Christoff    2000-04-29

