On Mar 8, 2011, at 11:56 AM, Josh Hykes wrote:
> At some point in my code, I need to do a cell-wise multiplication of the
> properties with a state variable. The ideal method would (1) be fast (no
> Python loops) and (2) not waste memory constructing an entire property map.
> My best attempt using choose does (1) but not (2).
Would the "out" keyword of np.choose be a possible solution? Using that, you
should be able to create the properies_map in place, and perhaps you can then
do the multiplication with the state variables in place also:
import numpy as np
properties = {0: 0.5, 1: 2.} # 2 materials
mesh_map = np.array([[0,0,0,0], [0,1,1,0], [0,1,1,0], [0,0,0,0]]) # 4x4 mesh
state_variables = np.arange(mesh_map.size).reshape(mesh_map.shape) # fake state
variables
answer = np.empty (mesh_map.shape, np.float) # do this only once with dtype of
properties
np.choose(mesh_map, (properties[0], properties[1]), out=answer)
answer[:] = answer * state_variables
Hope this helps,
Lutz
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