Ramanujan theta function

Named after mathematician Srinivasa Ramanujan.

the Ramanujan theta function

1. (mathematics) A theta function that generalizes the form of the Jacobi theta functions while capturing their general properties. It is defined as: ${\displaystyle f(a,b)=\sum _{n=-\infty }^{\infty }a^{\frac {n(n+1)}{2}}\;b^{\frac {n(n-1)}{2}}}$ for |ab| < 1.