% Evaluates conductivity 
%
% Arguments:
% z  matrix of complex-valued evaluation points
%
% Samuli Siltanen April 2012

function ans = sigma(z)

rho    = 3/4;
alpha  = 5;
rr     = abs(z);
ind    = (abs(rr)<(rho-1e-13));
r      = rr(ind);
F      = zeros(size(rr));
F(ind) = (r.^2-rho^2).^4.*(1.5-cos(3*pi*r/(2*rho)));
ans    = (1+alpha*F).^2; 

