Hi, Sorry if this is a double post - unsure if it made it the first time: Here are some timings that puzzle me a bit. Sum the two rows of a 2xn matrix, where n is some large number python -m timeit -s "from numpy import array,sum,reshape; x = array([1.5]*1000); x = reshape(x,(2,500))" "x.sum(0)" 10000 loops, best of 3: 36.2 usec per loop python -m timeit -s "from numpy import array,sum,reshape; x = array([1.5]*1000); x = reshape(x,(2,500))" "x[0] + x[1]" 100000 loops, best of 3: 5.35 usec per loop The two calculations are completely equivalent (at least from the numerical results point of view). But using the built-in sum() function is app. 6 times slower. Just for the reference - using Numeric gives python -m timeit -s "from Numeric import array,sum,reshape; x = array([1.5]*1000); x = reshape(x,(2,500))" "sum(x)" 100000 loops, best of 3: 7.08 usec per loop Any suggestions to why this might be - or am I doing something wrong here? Thanks // Mads PS. Thanks to everybody that responded to my previous posting on problems and questions regarding rint() and related coding issues. Your replies were very helpful!