You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: pr_spm_non_sphericity.m
    path of file: ./repos/malini/Codes/deconvolution - model/spm8/marsbar-0.44/@mardo_5/private
    
    the code of the file until where you have to start completion: function [xVi] = pr_spm_non_sphericity(xVi)
% return error covariance constraints for basic ANOVA designs
% FORMAT [xVi] = pr_spm_non_sphericity(xVi)
%

    
function [xVi] = pr_spm_non_sphericity(xVi)
% return error covariance constraints for basic ANOVA designs
% FORMAT [xVi] = pr_spm_non_sphericity(xVi)
%
% required fields:
% xVi.I    - n x 4 matrix of factor level indicators
%              I(n,i) is the level of factor i for observation n
% xVi.var  - 1 x 4 vector of flags
%              var(i) = 1; different variance among levels of factor i
% xVi.dep  - 1 x 4 vector of flags
%              dep(i) = 1;      depend