...
    
p0 = [0.5, 6.0];
[pest, ps, mses] = gradientdescent(time, voltage, @exp2func, p0, 1.0, 0.00001);
fprintf('c=%4.1fmV, tau=%4.1fms\n', pest(1), pest(2));

subplot(1, 2, 1);
hold on;
%surface(cs, taus, msesurf);
%plot3(ps(1,:), ps(2,:), mses, '.r');
%view(80, 35);
contourf(cs, taus, log10(msesurf));
plot(ps(1,:), ps(2,:), '.r');
hold off;
xlabel('c [mV]')
ylabel('tau [ms]')
zlabel('mse [mV^2]')

subplot(1, 2, 2);
hold on;
plot(time, voltage)
plot(time, exp2func(time, pest), 'LineWidth', 2)
hold off;
xlabel('time [ms]')
ylabel('voltage [mv]')
savefigpdf(gcf, 'exp2plot.pdf', 15, 8.5);