Rewrite mesh_grid to be less compact but 100x faster.

Most of the time required to build the LBNE geometry is spent on
mesh_grid() for the highly segmented cylinder.  (67 seconds!)  The
speed hit is caused by the use of zip to connect the vertices.  The
same task can be done in several lines with slice notation, and goes
much faster.

1 files changed, 14 insertions, 1 deletions

diff --git a/chroma/make.py b/chroma/make.py
index 2c3155a..2f1d9a5 100644
--- a/chroma/make.py
+++ b/chroma/make.py
@@ -4,7 +4,20 @@ from chroma.transform import rotate
 from chroma.itertoolset import *
 
 def mesh_grid(grid):
-    return np.vstack(zip(grid[:-1].flatten(),grid[1:].flatten(),np.roll(grid[1:],-1,1).flatten()) + zip(grid[:-1].flatten(),np.roll(grid[1:],-1,1).flatten(),np.roll(grid[:-1],-1,1).flatten()))
+    begin = grid[:-1].flatten()
+    end = grid[1:].flatten()
+    begin_roll = np.roll(grid[:-1],-1,1).flatten()
+    end_roll = np.roll(grid[1:],-1,1).flatten()
+    
+    mesh = np.empty(shape=(2*len(begin),3), dtype=begin.dtype)
+    mesh[:len(begin),0] = begin
+    mesh[:len(begin),1] = end
+    mesh[:len(begin),2] = end_roll
+    mesh[len(begin):,0] = begin
+    mesh[len(begin):,1] = end_roll
+    mesh[len(begin):,2] = begin_roll
+
+    return mesh
 
 def linear_extrude(x1, y1, height, x2=None, y2=None, center=None):
     """