On odd rank integral quadratic forms: canonical representatives of projective classes and explicit construction of integral classes with square-free determinant

Abstract

Two rank n, integral quadratic forms f and g are said projectively equivalent if there exist nonzero rational numbers r and s such that rf and sg are rationally equivalent. Two odd dimensional, integral quadratic forms f and g are projectivelly equivalent if and only if their adjoints are rationally equivalent. We prove that a canonical representative of each projective class of forms of odd rank, exists and is unique up to genus (integral equivalence for indefinite forms). We give a useful characterization of this canonical representative. An explicit construction of integral classes with square-free determinant is given. As a consequence, two tables of ternary and quinary integral quadratic forms of index 1 and with square-free determinant are presented.