Should support Linear Angle parse

[liuyujie714]

Issue

MDAnalysis currently can not support parse Linear Angle from GROMACS .tpr file.

Additional context

For example, for CO2 molecule, has angle potential:

[ angles ]
2 1 3 9 0.5 220066

Solution

add LINEAR_ANGLES to

mdanalysis/package/MDAnalysis/topology/tpr/utils.py

Lines 827 to 829 in 3be9117

	elif ik_obj.name in ['ANGLES', 'G96ANGLES', 'CROSS_BOND_BOND',
	'CROSS_BOND_ANGLE', 'UREY_BRADLEY', 'QANGLES',
	'RESTRANGLES', 'TABANGLES']:

[orbeckst]

Does this lead to a failure when reading a TPR file?

[tylerjereddy]

There would be value in providing a sample .tpr file to start with, and perhaps a short description of what it might look like in MDAnalysis to have access to this information.

[liuyujie714]

There would be value in providing a sample .tpr file to start with, and perhaps a short description of what it might look like in MDAnalysis to have access to this information.

I provided a single CO2 molecule example:
CO2.zip

gmx grompp -c CO2.gro -f nvt.mdp -o Linear_Angle.tpr

Then issue,

import MDAnalysis as mda
u = mda.Universe('Linear_Angle.tpr')
print(u.angles.to_indices())

Output [], but correct result should be [[1 0 2]]