Properties of reciprocity formulas for the Rogers–Ramanujan continued fractions

Abstract

Ramanujan recorded four reciprocity formulas for the Roger-Ramanujan continued fractions. Two reciprocity formulas each are also associated with the Ramanujan-Göllnitz-Gordon continued fractions and a level-13 analog of the Roger-Ramanujan continued fractions. We show that all eight reciprocity formulas are related to a pair of quadratic equations. The solution to the first equation generalizes the golden ratio and is used to set the value of a coefficient in the second equation; and the solution to the second equation gives a pair of values for a continued fraction. We relate the coefficients of the quadratic equations to important formulas obtained by Ramanujan, examine a pattern in the relation between a continued fraction and its parameters, and use the reciprocity formulas to obtain close approximations for all values of the continued fractions. We highlight patterns in the expressions for certain explicit values of the Rogers-Ramanujan continued fractions by expressing them in terms of the golden ratio. We extend the analysis to reciprocity formulas for Ramanujan's cubic continued fraction and the Ramanujan-Selberg continued fraction.Roger-Ramanujan continued fractions and Ramanujan-Göllnitz-Gordon continued fractions and Ramanujan's cubic continued fractions and Ramanujan-Selberg continued fraction and Reciprocal formulas Date