So if you take the summoner as a secondary class with the new unchained book, it tells you you lose half of your evolutions. Is that half of the free evolutions? half of all evolutions-to include your automatically assigned ones? If it is half of your automatic ones--how do you determine which ones?
Are you talking about variant multiclassing?
If so, than the entry for Eidolon states: "Eidolon: At 7th level, he gains the ability to summon an eidolon, using the statistics of an eidolon for a summoner of his character level – 4, except with half as many evolution points. This eidolon can only be summoned using his summon monster spell-like ability."
This simply means that you have half the normal evolution points. For example, when you gain this ability at level 7, the number of points is calculated as if you were a summoner of level 3, cut in half. From the table, a level 3 summoner gets an eidolon with 5 evolution points, so you'd get one with 2 evolution points. (2.5 rounded down)
It says evolution points, not evolutions. So it is only the points you need to reduce, not the ones you get without spending points on them.
Thank you