function mostra_elemento_zero(A0,NP)

k = 0; 
for ix = 1:NP(1)
    for iy = 1:NP(2)
        k = k + 1;
        xg(ix,iy) = ix - 1;
        yg(ix,iy) = iy -1 ;
        A0k = full(A0(k));
        if A0k == 0
            fg(ix,iy) = -20;
        else
            fg(ix,iy) = log10(A0k);
        end
    end
end
figure(77)
surf(xg,yg,fg)