Manual entry for abs function of vector space algebra differs from implementation

[jan@…]

The manual entry for a vector space algebra definition in boost odeint states that the return value of the abs function necessary for controlled steppers must be of state type. http://www.boost.org/doc/libs/1_66_0/libs/numeric/odeint/doc/html/boost_numeric_odeint/odeint_in_detail/state_types__algebras_and_operations.html#boost_numeric_odeint.odeint_in_detail.state_types__algebras_and_operations.algebras_and_operations.vector_space_algebra This works only for fundamental types as described in the following stackoverflow entry. ​https://stackoverflow.com/questions/44566641/boost-odeint-controlled-stepper-with-custom-class-and-vector-space-algebra For custom types it only compiles when the return value of the abs function is of value type. This would also correspond to the mathematical understanding of the absolute value defined in a vector space.