    function [Fmap] = wfu_bpm_compute_Fmap(BETA_slice,XtX,c,Rc,brain_mask,sig2,Fmap,M,N,nr)
    %---------- computing Fmaps for regression ------------------%
    for m = 1:M
        for n = 1:N
            if brain_mask(m,n) == 1
                if sig2(m,n) > 0
                    beta = BETA_slice(m,n,:);
                    beta = beta(:);
                    SSres = (n-nr)*sig2(m,n);
                    X_pinv = pinv(reshape(XtX(m,n,:),nr,nr));
                    SSc = ((beta'*c)*pinv(c'*X_pinv*c)*(c'*beta))/Rc;
                    q = nnz(c);
                    Fmap(m,n) = (SSc/q)/(SSres/(n-nr));

    %                 beta = BETA_slice(m,n,:);
    %                 beta = beta(:);
    %                 num = ((beta'*c)*pinv(c'*X_pinv*c)*(c'*beta))/Rc;
    %                 Fmap(m,n) = num/sig2(m,n);
                end
            end
        end
    end

    Input argument "M" is undefined.

    Error in ==> wfu_bpm_compute_Fmap at 3
    for m = 1:M