Hi David,
Thanks for the tip.
I tried your suggestions and I still get an error:
Leaving out the transpose gives the same result as before:
>>> for a in mol.atoms:
... newpos = mol.atom(a.index).pos * R;
... mol.atom(a.index).pos = newpos
...
Traceback (most recent call last):
File "<string>", line 1, in <module>
SystemError: NULL result without error in PyObject_Call
You suggestion to simplify the loop also gives an error, but a different one:
>>> for a in mol.atoms:
... a.pos = R * a.pos
...
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/usr/lib/python2.6/dist-packages/numpy/core/defmatrix.py", line 290, in
__mul__
return N.dot(self, asmatrix(other))
ValueError: matrices are not aligned
>>>
I'm afraid I don't know how to interpret the error messages. Any advice would
be appreciated.
Thanks,
Steve
________________________________________
From: David Lonie [[email protected]]
Sent: Tuesday, July 26, 2011 8:12 PM
To: Steven Wathen
Cc: Avogadro-devel Devel
Subject: Re: [Avogadro-devel] using python console to rotate a molecule in
Avogadro
On Tue, Jul 26, 2011 at 7:49 PM, Steven Wathen <[email protected]> wrote:
> Hello,
>
> I have been experimenting with the Avogadro python interface and I have a
> question. I am trying to rotate the whole molecule, and after googling a bit
> I came up with a procedure that I think should work, but gives an error when
> I run it.
>
> To start with I used the GUI to build and minimize chloromethane, then I
> entered this into the Python console:
>
>>>> import Avogadro
>>>> import numpy
>>>> import math
>
>>>> mol = Avogadro.molecule
>>>> a = math.cos( math.radians(-30.0) )
>>>> b = math.sin( math.radians(-30.0) )
>>>> R = numpy.mat( [[a, -b, 0], [b, a, 0], [0,0,1]] )
>>>> for a in mol.atoms:
> ... newpos = mol.atom(a.index).pos * R;
> ... newpos = newpos.T;
> ... mol.atom(a.index).pos = newpos
> ...
> Traceback (most recent call last):
> File "<string>", line 1, in <module>
> SystemError: NULL result without error in PyObject_Call
>>>>
>
> Just to see if I could get something that works I picked an arbitrary angle
> of -30 degrees. I am afraid that my matrix algebra skills are quite out of
> date and I could be misunderstanding something simple about the mathematics
> or about numpy.
In C++, the Atom::pos() function returns an Eigen vector, which is by
default a column vector. I'm not sure what is returned in python, but
try
newpos = R * mol.atom(a.index).pos
mol.atom(a.index).pos = newpos
and see if that clears it up. The transpose shouldn't be necessary.
If I remember python correctly, You may be able to replace
"mol.atom(a.index).pos" with just "a.pos", unless the python wrappers
are doing something unexpected. If so, you may be able write the
entire loop body as
a.pos = R * a.pos
Hope this helps,
Dave
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