It is possible to connect systems using the `YopConnection`

command. The purpose of this is to simplify creating an initial guess for non-convex optimal control problems. By connecting your system to a controller, it is possible to create an initial guess by simulation, even for an unstable system. Despite being the main purpose, connecting the system to a controller is not the only use for connections.

## Declaration

Connections are declared using the following syntax:

```
c = YopConnection(arg1, arg2);
```

The input arguments `arg1`

, and `arg2`

can be any symbolic expression that can be formulated using the system variables `t`

, `x`

, `z`

, `u`

, `w`

, `p`

, `ode`

, `ae`

, and `y`

(see YopSystem for a description of them). `arg1`

and `arg2`

can be vector valued as long as they have the same dimension. The output argument `c`

is a handle to the connection.

## What a `YopConnection`

is

A `YopConnection`

is an algebraic constraint stating

This means that the following declarations are equivalent:

```
c1 = YopConnection(arg1, arg2);
c2 = YopConnection(arg1-arg2, zeros(size(arg1-arg2)));
c3 = YopConnection(zeros(size(arg1-arg2)), arg1-arg2);
```