function A=getEffSigma(sigma,esp,freq)
%computes effective azimuthal anisotropic (see Josef Pek et al., 2002). conductivity
if nargin == 1
    A.xx = sigma(:,1) - (sigma(:,5).^2) ./ sigma(:,3);
    A.yy = sigma(:,2) - (sigma(:,6).^2) ./ sigma(:,3);
    A.xy = sigma(:,4) - (sigma(:,5) .* sigma(:,6)) ./ sigma(:,3);
elseif nargin == 3
    omega = 2 * pi * freq;
    iom   = 1i*omega;
    y1 = sigma(:,1)-iom.*esp(:,1);
    y2 = sigma(:,2)-iom.*esp(:,2);
    y3 = sigma(:,3)-iom.*esp(:,3);
    y4 = sigma(:,4)-iom.*esp(:,4);
    y5 = sigma(:,5)-iom.*esp(:,5);
    y6 = sigma(:,6)-iom.*esp(:,6);
    
    A.xx  = y1 - y5.^2 ./y3;
    A.yy  = y2 - y6.^2 ./y3;
    A.xy  = y4 - (y5.*y6) ./y3;
end