Re: vectorial manipulation

[Jean-Noël Grad]

Dear Shammi Babar,

You can use the following solution:

```python
p = system.part[0]
v = np.copy(p.v)
v[1] += 0.2
p.v = v
```

You can wrap this solution in a function to make the pypresso script 
more readable. Here is a minimal working example:

```python
import espressomd
import numpy as np

def update_particle_velocity(system, pid, v):
    p = system.part[pid]
    p.v = np.copy(p.v) + v

system = espressomd.System(box_l=[10, 10, 10])
system.part.add(id=1, pos=[0, 0, 0], v=[0, 0, 0])
update_particle_velocity(system, 1, [0.1, 0.2, 0.3])
print(system.part[1].v)
```

Best,
JN

On 2022-01-29 12:50, Shammi Babar wrote:
> dear espresso users,
>
> I have a question about vectorial particle properties in espresso. in
> fact I need to replace velocity of some specified particles with new
> values during simulation, but as explained in user guide:
> https://espressomd.github.io/doc4.1.4/particles.html (section 4.3.1)
> it is not allowed and will result in an error.
> could you please help me solve this issue?
>
> thanks