TMatrixD and PyRoot

ROOT
1

Hi,

I’m trying to create and manipulate a TMatrixD in PyRoot.

In Cint, I just do

root [1] TMatrixD cov(2,2)                                     
root [2] cov(0,0)
(double)0.00000000000000000e+00
root [3] cov(0,0)=1
(const int)1

But this doesn’t work in PyRoot:

>>> import ROOT
>>> cov = ROOT.TMatrixD (2,2)
>>> cov(0,0)
0.0
>>> cov(0,0) = 2
Are you trying to assign a value to a reference return, for example to the
result of a call to "double& SMatrix<>::operator()(int,int)"? If so, then
please use operator[] instead, as in e.g. "mymatrix[i,j] = somevalue".

  File "<stdin>", line 1
SyntaxError: can't assign to function call
>>>

As far as I can tell, the only way to set the matrix is by calling operator() which returns a reference. But this doesn’t work in Python, so what can I do?

Thanks,
Charles

2

Charles,

it’s possible in a round-about way through “cov[0][0] = 2”. It’ll be very slow due to the creation of many temporaries, though.

Cheers,
Wim