numpy-discussion

[Numpy-discussion] degree matrix construction

[Satya U. <sat...@ya...>]

Dear Friends,
my question is the following:

Suppose i have the following code:

>>> from LinearAlgebra import *

>>> from Numeric import *
>>> A = [1,2,1,3,1,3,4,1,2]
>>> B = reshape(A,(3,3))
>>> C = sum(B,1)
>>> C
array([4, 7, 7])
>>> 

Now, my problem is to construct a degree matrix D which is a 3 * 3 matrix with diagonal elements 4,7,7 (obtained from the elements of C) and all off-diagonal elements equal to 0.
Could some kind soul kindly tell me how to do this.
I've looked at the help for the diagonal function and i am unable to do what i wish to. Furthermore i dont understand the meaning of axis1 and axis2:
>>> help (diagonal)
Help on function diagonal in module Numeric:

diagonal(a, offset=0, axis1=0, axis2=1)
    diagonal(a, offset=0, axis1=0, axis2=1) returns all offset diagonals
    defined by the given dimensions of the array.

>>>

Thanking you,
Satya




 				
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Re: [Numpy-discussion] degree matrix construction

[Joris De R. <jo...@st...>]

Hi,

   [SU]: Now, my problem is to construct a degree matrix D which is a 3 * 3 matrix with diagonal elements 4,7,7 

You might have a look at the Numpy Example List, at the function diag().

Ciao,
Joris


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Re: [Numpy-discussion] degree matrix construction

[Charles R H. <cha...@gm...>]

On 9/15/06, Satya Upadhya <sat...@ya...> wrote:
>
> Dear Friends,
> my question is the following:
>
> Suppose i have the following code:
>
> >>> from LinearAlgebra import *
>
> >>> from Numeric import *
> >>> A = [1,2,1,3,1,3,4,1,2]
> >>> B = reshape(A,(3,3))
> >>> C = sum(B,1)
> >>> C
> array([4, 7, 7])
> >>>
>
> Now, my problem is to construct a degree matrix D which is a 3 * 3 matrix
> with diagonal elements 4,7,7 (obtained from the elements of C) and all
> off-diagonal elements equal to 0.
>

Is this what you want to do?

In [2]: a = array([4, 7, 7])

In [3]: diagflat(a)
Out[3]:
array([[4, 0, 0],
       [0, 7, 0],
       [0, 0, 7]])

Chuck