Rotate an object around pivot point by using Matrices

Questions
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1

In this post, i found an answer, how to rotate an object around a pivot point: How to rotate an object around a pivot point?

My problem is, i have a Matrix4 and i have to rotate my object with this Matrix4.
This can be done by obj.applyMatrix(M).

Now i need to rotate the object not around its center but around a pivot point…
I tried it with the strategy above and at the end calling this:
pivot.applyMatrix(M) instead. It seems like the Matrix doesnt care about that point or group and just turning the object again around its center. Does anybody understand the matrices and its rotations and can anybody give me a hint?

2

Maybe you can find in the following discussion at github something useful: