[mesa-users] [GYRE] Interpretation of xi_r

[alfred at gautschy.ch]

Cyrus

xi_r is the radial displacement function, a complex quantity (see  
appendix of GYRE method paper MNRS 435, 3406 (2013) or Unno et al.  
monograph, "Nonradial oscillations of stars" where the same definition  
of the quantities is used). As usual in physics, the real part of the  
quantity is interpreted as the "physical component".

xi_r is *not* a relative perturbation, but of course you are free to  
define one, such as xi_r/r, which is frequently used in radial  
pulsation modeling. Finally,  you are free to choose the normalization  
of your solution, after all it's a linear problem. Frequently you find  
that the displacement at the surface is arbitrarily set to unity.

Alfred