Scripts: Get Anger Level

Does anyone know a way to find the anger level of one empire towards another? The scripting manual has a formula to SET this anger level to a specific value (Sys_Empire_Politics_Set_Anger_Pct_Towards_Empire:). What I WANT to do is to look up what the value is already and adjust it by a certain amount or percent - not just simply plug in a new value with no knowledge of what the previous value was.

Is there a way to do this? I can't find a function that will find this information.

Thanks