Add a function for calculating proper distance.

1 files changed, 19 insertions, 0 deletions

diff --git a/invars.py b/invars.py
new file mode 100644
index 0000000..7937108
--- /dev/null
+++ b/invars.py
@@ -0,0 +1,19 @@
+import numpy             as np
+import scipy.interpolate as interp
+import scipy.integrate   as integrate
+
+def calc_dist_proper(coord, gXX):
+    """
+    Calculate proper distance along given spatial axis.
+
+    :param array_like coord: 1D array of spatial coordinates.
+    :param array_like gXX: Values of the XX component of the spatial metric at
+                           provided coordinates.
+    :return: array of proper distances from coord[0].
+    """
+    r_proper = np.empty_like(coord)
+    sqgXX    = interp.interp1d(coord, np.sqrt(gXX))
+    r_proper[0] = 0.0
+    for i in xrange(coord.shape[0] - 1):
+        r_proper[i + 1] = r_proper[i] + integrate.quad(sqgXX, coord[i], coord[i + 1])[0]
+    return r_proper