How do I perform one level of Romberg integration on an integral I using the results for $\displaystyle T_m$ and $\displaystyle T_{2m}$ as level 0? $\displaystyle T_m$ denotes an approximation to I using the composite trapezium rule with m strips.

I will be doing it in MATLAB but I'm not looking for code - just help or a link to a formula.

Thanks!