optimization formulas latex
documentclass{article}
usepackage{amsmath}
begin{document}
begin{equation}
begin{aligned}
min_{w,b,xi} quad & frac{1}{2}w^{t}w+Csum_{i=1}^{N}{xi_{i}}\
textrm{s.t.} quad & y_{i}(wphi(x_{i}+b))+xi_{i}-1\
&xigeq0 \
end{aligned}
end{equation}
end{document}