How to set velocity manually

[secretqsan]

Can I set the velocities in a universe manually? I tried by the following code:
for ts in u.trajectory:
v = np.array(np.loadtxt(f'velocity_{ts.frame}.dat'))
ts.velocities = v
but the velocities of all the frames are equal to the last frame. How can I do this properly?

[p-j-smith]

Hi @secretqsan, velocities would typically be read automatically when you call MDAnalysis.Universe if you have a trajectory file format that supports velocities (such as .trr, .ncdf, and .gro files).

If you would like to set your velocities manually, you will need to load your trajectory into memory. However, you will still need to use a trajectory format that supports velocities, otherwise you will run into the issue you are seeing.