(@PRE-FORCES-target)=
# @PRE-FORCES
Go to point in code where forces have been partially calcualted.



## @FORCES

Go to @PRE-FORCES node.


 The engine proceeds to the next @PRE-FORCES node. 
This node occurs after calculating all contributions to the atomic forces, except those associated with a constraint algorithm like SHAKE or RATTLE.
This command is not valid at the [@DEFAULT](#@DEFAULT) node.
One would typically proceed to the @FORCES node after initializing a simulation 
(e.g. [@INIT_MD](#@INIT_MD), [@INIT_MC](#@INIT_MC), or [@INIT_OPTG](#@INIT_OPTG)).


### Examples


::::{tab-set}

:::{tab-item} Python
:sync: python

```python
import mdi

# connect to the engine
mdi_engine = mdi.MDI_Accept_Communicator()

# first initialize a simulation
mdi.MDI_Send_Command("@INIT_MD", mdi_engine)

# go to forces node
mdi.MDI_Send_Command("@PRE-FORCES", mdi_engine)

```
:::

:::{tab-item} C++
:sync: cpp

```cpp
#include "mdi.h"

// connect to the engine
MDI_Comm mdi_engine = MDI_Accept_Communicator();

// first initialize a simulation
MDI_Send_Command("@INIT_MD", mdi_engine);

// go to forces node.
MDI_Send_Command("@PRE-FORCES", mdi_engine);

```
:::

::::