Magnetogasdynamic shock polar for aligned fields

An equation for magnetogasdynamic shock polar, given in terms of magnetic induction polar variables (i.e. the magnetic induction polar), is obtained. Evolutionary and entropy non-decrease conditions, given in terms of these polar variables, assume a very simple form, and admit immediate geometrical interpretation. It is found that this magnetic induction polar is far more natural and convenient to use than the shock polar given in terms of conventional velocity polar variables.