How can I calculate a multi-axis SCNVector4 rotation for a SCNNode?

Question

The SCNNode take a rotation using a SCNVector4, which has an angle (w) and a magnitude how that angle applies to each axis (x, y, z). For example, to rotate 45

Answer 1

Do you ask for rotation matrix or how to simply rotate in general? If the second is correct then for example:

[node runAction:[SCNAction rotateByX:0 y:M_PI z:0 duration:0]];