Duplicate entries in a matrix

[Gerard Flanagan]

Chris Lasher wrote:

> Hello Pythonistas!
>   I'm looking for a way to duplicate entries in a symmetrical matrix
> that's composed of genetic distances. For example, suppose I have a
> matrix like the following:
>
>   A        B        C
> A 0.000000 0.500000 1.000000
> B 0.500000 0.000000 0.500000
> C 1.000000 0.500000 0.000000
>
> Say I want to duplicate entry B; the resulting matrix would look like:
>
>   A        B        B        C
> A 0.000000 0.500000 0.500000 1.000000
> B 0.500000 0.000000 0.000000 0.500000
> B 0.500000 0.000000 0.000000 0.500000
> C 1.000000 0.500000 0.500000 0.000000
>
> The cases I'd like to do this for are more complicated, naturally,
> where I want to duplicate different entries different numbers of times.
> I'm aware of Numeric, Numarray, and NumPy, though I've not used any of
> them, but I am not sure if any of them possess a simple means to
> duplicate entries in a matrix. I started writing code on my own but I
> can see it is becoming exponentially more complex, and before I proceed
> any further, I want to make sure I'm not reinventing any wheels. If
> anyone here has any advice on how to manipulate matrices in this
> manner, I'd _greatly_ appreciate it!
>
> Thanks in advance,
> Chris

Chris

Very rusty at this sort of thing, but if you premultiply the first
matrix by:

1  0  0
0  1  0
0  1  0
0  0  1

and postmultiply the result by:

1  0  0  0
0  1  1  0
0  0  0  1

I think you get what you want. (If that helps).

Gerard