from matplotlib.matlab import *
plot([1,2,3])
xlabel(r'$\Delta_i$')
ylabel(r'$\Delta_{i+1}$')
tex = r'$\cal{R}\prod_{i=\alpha_{i+1}}^\infty a_i\rm{sin}(2 \pi f x_i)$'
text(0.4, 2.6, tex, fontsize=20)
title(r'$\Delta_i\rm{ versus }\Delta_{i+1}$', fontsize=15)
savefig('mathtext_demo', dpi=100)
show()