numpy - 2D matrix/array - initialization like in Matlab...

[MRAB]

On 2012-10-15 22:09, someone wrote:
>
> See this:
>
> ==========================================================
> In [5]: Dx = numpy.matrix('1 0 0; 0 0.5 -0.5; 0 -0.5 1.5')
>
> In [6]: Dx
> Out[6]:
> matrix([[ 1. ,  0. ,  0. ],
>           [ 0. ,  0.5, -0.5],
>           [ 0. , -0.5,  1.5]])
> ==========================================================
>
>
>
> Ok... So now test = 33 and instead of the value 1.5 I want to use the
> value of "test" and put it directly into the matrix (or array):
>
> ==========================================================
> In [7]: test=33
>
> In [8]: Dx = numpy.matrix('1 0 0; 0 0.5 -0.5; 0 -0.5 test')
> ---------------------------------------------------------------------------
> NameError                                 Traceback (most recent call last)
> /home/user/something/<ipython-input-8-5a43575649e1> in <module>()
> ----> 1 Dx = numpy.matrix('1 0 0; 0 0.5 -0.5; 0 -0.5 test')
>
> /usr/lib/python2.7/dist-packages/numpy/matrixlib/defmatrix.pyc in
> __new__(subtype, data, dtype, copy)
>       252
>       253         if isinstance(data, str):
> --> 254             data = _convert_from_string(data)
>       255
>       256         # now convert data to an array
> ...... etc...
> ==========================================================
>
>
>
> So obviously it doesn't understand that I want this:
>
> ==========================================================
> In [21]: Dx[2,2]=test
>
> In [22]: Dx
> Out[22]:
> matrix([[  1. ,   0. ,   0. ],
>           [  0. ,  33. ,  -0.5],
>           [  0. ,  -0.5,  33. ]])
> ==========================================================
>
> Without having to manually change all the individual places using my
> variables (test is actually many variables, not just one but I think you
> should understand the problem now).
>
>
> How to initialize my array directly using variables ?
>
> It could also be that I wanted:
>
> test11 = 1
> test12 = 1.5
> test13 = 2
> test21 = 0
> test22 = 5
>
> Dx = numpy.matrix('test11 test12 test13; test21 test22 -0.5; 0 -0.5 1.5')
>
> Etc... for many variables...
>
> Appreciate ANY help, thank you very much!
>
What it prints should give you a hint:

 >>> Dx = numpy.matrix([[test11, test12, test13], [test21, test22, 
-0.5], [0, -0.5, 1.5]])
 >>> Dx
matrix([[ 1. ,  1.5,  2. ],
         [ 0. ,  5. , -0.5],
         [ 0. , -0.5,  1.5]])