On 10/16/07, Julien Hillairet <[EMAIL PROTECTED]> wrote: > > Hello, > > > First of all, I'm sorry if this question had already been asked. I've > searched on the gmane archive and elsewhere on internet, but I didn't found > the answer to my question. > > As expected, the dot product of 2 'classical' vectors works fine : > > In [50]: a0 = numpy.array([1,2,3]) > In [51]: numpy.dot(a0,a0) > Out[51]: 14 > > What I don't understand, is why the dot product of a (3,N) vector gives an > error : > > In [52]: a1 = numpy.array([[1,2,3],[1,2,3],[1,2,3],[1,2,3]]) > In [54]: numpy.dot(a1,a1) > <type 'exceptions.ValueError'> Traceback (most recent call > last) > <type 'exceptions.ValueError'>: objects are not aligned > > instead of what I've expected ; an array([14 14 14 14]). > > Of course, I've found an alternative in doing : > > In [61]: numpy.sum(a1*a1,axis=1) > Out[61]: array([14, 14, 14, 14]) > > But I like to understand my mistakes or misunderstands :) So, could > someone explained me what I've missed ? Thanks in advance.
Dot is matrix multiplication, not the "dot" product you were expecting. It is also a bit ambiguous, as you see with the 1-D vectors, where you got what you expected. Chuck
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