M = [-2:0.05:2];
plot(M,tanh(2*M),M,tanh(M),M,tanh(M/2),M,tanh(M/5),M,M,'k')
set(gca,'ylim',[-1.5 1.5])
set(gca,'ylim',[-1.2 1.2])
legend('\mu=2','\mu=1','\mu=1/2','\mu=1/5');
xlabel 'M'
ylabel 'tanh (\mu M)'

mu = [0.7:0.002:0.998];
Mstar = zeros(size(mu));

g = @(x,c) x - tanh(c*x);

for m=1:length(mu);
    
    c = 1/mu(m);

    Mstar(m) = fzero(@(x) g(x,c),[0.01 1.1]);
    
end

Mstar (end+1) = 0;
mu = [mu 1];
mu2 = [1:0.01:1.2];

plot(mu,[Mstar; -Mstar],'b',mu,zeros(size(mu)),'b--',mu2,zeros(size(mu2)),'b');
set(gca,'xlim',[0.7 1.2]);
xlabel 'T/T_c'
ylabel 'M^*'
axis square