Determine lattice speed of sound

1 files changed, 6 insertions, 0 deletions

diff --git a/symbolic/characteristics.py b/symbolic/characteristics.py
index ca3904e..b68afeb 100644
--- a/symbolic/characteristics.py
+++ b/symbolic/characteristics.py
@@ -19,3 +19,9 @@ def gauss_hermite(n):
 def weights(d, c):
     _, omegas = gauss_hermite(3)
     return list(map(lambda c_i: Mul(*[ omegas[1+c_i[iDim]] for iDim in range(0,d) ]) / pi**(d/2), c))
+
+# determine lattice speed of sound using directions and their weights
+def c_s(d, c, w):
+    speeds = set([ sqrt(sum([ w[i] * c_i[j]**2 for i, c_i in enumerate(c) ])) for j in range(0,d) ])
+    assert len(speeds) == 1 # verify isotropy
+    return speeds.pop()