Wronskians of theta functions and series for $1/\pi$
  In this article, we define functions analogous to Ramanujan's function $f(n)$ defined in his famous paper "Modular equations and approximations to $\pi$". We then use these new functions to study Ramanujan's series for $1/\pi$ associated with the classical, cubic and quartic bases. 
Alex Berkovich, Heng Huat Chan and Michael J. Schlosser
math.NT