atan Arc tangent &reftitle.description; floatatan floatarg Returns the arc tangent of arg in radians. atan is the complementary function of tan, which means that a==tan(atan(a)) for every value of a that is within atan's range. &reftitle.parameters; arg The argument to process &reftitle.returnvalues; The arc tangent of arg in radians. &reftitle.seealso; tan atanh asin acos