# [SciPy-user] about the addition of several sparse matrix

Zhang Sam hollowspook at gmail.com
Mon Dec 4 07:52:30 CST 2006

```Hi, there

I have several sparse matrices in coo_matrix format, say Y1, Y2, Y3, Y4. I
want to get the sum of them and I use the operation:  Y = Y1 + Y2 + Y3 +
Y4.

When I print Y, it returns:
>>>   (0, 0) -17.3611111111j
(3, 0) 17.3611111111j
(1, 1) -16j
(7, 1) 16j
(2, 2) -17.0648464164j
(5, 2) 17.0648464164j
(0, 3) 17.3611111111j
(3, 3) (1.94219124871-27.792793163j)
(3, 3) (1.36518771331-11.5160955631j)
(4, 3) (-1.94219124871+10.5106820519j)
(8, 3) (-1.36518771331+11.6040955631j)
(3, 4) (-1.94219124871+10.5106820519j)
(4, 4) (3.22420038714-15.8409270142j)
(5, 4) (-1.28200913842+5.58824496236j)
(2, 5) 17.0648464164j
(4, 5) (-1.28200913842+5.58824496236j)
(5, 5) (1.15508748089-26.7446168427j)
(5, 5) (1.28200913842-5.40924496236j)
(6, 5) (-1.15508748089+9.78427042636j)
(5, 6) (-1.15508748089+9.78427042636j)
(6, 6) (2.77220995414-23.3032490233j)
(7, 6) (-1.61712247325+13.6979785969j)
(1, 7) 16j
(6, 7) (-1.61712247325+13.6979785969j)
(7, 7) (1.61712247325-29.6234785969j)
(7, 7) (1.18760437929-5.82213453331j)
(8, 7) (-1.18760437929+5.97513453331j)
(3, 8) (-1.36518771331+11.6040955631j)
(7, 8) (-1.18760437929+5.97513453331j)
(8, 8) (2.5527920926-17.3382300964j)

It is strange that there are two (3,3) entries, two (5,5) entries and two
(7,7) entries. I have checked this result. It is correct if we add the
two value together. What operation can let it return a sparse matrix
which has only one value at every nonzero entry?

Thanks!

Sam
Dec 4th, 2006
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