If you increment an array using advanced indexing and have repeated indexes, the array doesn't get repeatedly incremented, http://comments.gmane.org/gmane.comp.python.numeric.general/50291. I wrote a C function that does incrementing with repeated indexes correctly. The branch is here (https://github.com/jsalvatier/numpy see the last two commits). Would a patch with a cleaned up version of a function like this be accepted into numpy? I'm not experienced writing numpy C code so I'm sure it still needs improvement.

from numpy import *

from numpy.core.multiarray import index_increment

a = arange(12).reshape((3,4))

index = ([1,1,2,0], [0,0,2,3])

vals = [50,50., 30.,16]

b = index_increment(a, index, vals)

print b