function [u0, l0, D0] = material_paras(e0, nu0)
    u0 = 0.5*e0/(1+nu0);
    l0 = e0*nu0/((1+nu0)*(1-2*nu0));
    l0 = 2*u0*l0/(l0+2*u0); % 2d lame paras!!!!
    
    D0 = e0/(1-nu0^2)*[1 nu0 0; nu0 1 0; 0 0 (1-nu0)/2];
end