Added script trying to decompose the stellar population

density_center.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+import numpy as np
+
+def def_dc(m, x, v=None, r_min=0.0045):
+    """
+    Calculates the center of density. Translated to Python from phiGRAPE.
+
+    Parameters
+    ----------
+    m, x, v : array_like
+        Particle parameters. v is optional.
+    r_min : scalar
+        For star clusters, should be 0.1 pc in N-body units.
+
+    Returns
+    -------
+    xdc, vdc : ndarrays
+    """
+    calc_vdc = not v is None
+    x_ = x.copy()
+    xdc = np.zeros(3)
+    if calc_vdc:
+        v_ = v.copy()
+        vdc = np.zeros(3)
+    else:
+      v_ = None
+    r_lim = np.sqrt(np.max(np.sum(x**2, axis=1)))
+    num_iter = 0
+
+    while (r_lim > r_min) and (num_iter < 100):
+        ncm, mcm, xcm, vcm = cenmas_lim(m, x_, v_, r_lim)
+        if((mcm > 0) and (ncm > 100)):
+            x_ -= xcm
+            xdc += xcm
+            if calc_vdc:
+              v_ -= vcm
+              vdc += vcm
+        else:
+            break
+        r_lim *= 0.8
+        num_iter += 1
+    if calc_vdc:
+        return xdc, vdc
+    else:
+        return xdc
+
+def cenmas_lim(m, x, v, r_lim):
+    r2 = np.sum(x**2, axis=1)
+    cond = r2 < r_lim**2
+    ncm = np.sum(cond)
+    mcm = np.sum(m[cond])
+    if mcm == 0: return ncm, 0., np.zeros(3), np.zeros(3)
+    xcm = np.sum(m[cond,None] * x[cond,:], axis=0) / mcm
+    if not v is None: vcm = np.sum(m[cond,None] * v[cond,:], axis=0) / mcm
+    else: vcm = None
+    return ncm, mcm, xcm, vcm