Update Modelica in Jupyter.ipynb

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# Modelica x Jupyter

These cells contain modelica code that can be run via Jupyter.

To install:

* Install OpenModelica

* Install Anaconda

* Create environment in `env.yml`

```

    conda env create -f env.yml

```

## Architecture

```

Modelica ->(compiler)-> Functional Mockup Unit ->(pyFMI)->(gym wrapper) -> RL

```

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``` OpenModelica

class Pendulum "Pendulum"

    Real F=0;                 // External force tengential to motion

    Real F;                 // Total force along pendulum string

    constant Real PI=3.141592653589793;

    parameter Real m=1, g=9.81, L=0.5;

    output Real x(start=0.5),y(start=0);

    output Real vx,vy;      // x and y velocities

equation

    // 5 variables, 5 equations

    m*der(vx)=-(x/L)*F;     // Force equation in x direction

    m*der(vy)=-(y/L)*F-m*g; // Force equation in y direction

    der(x)=vx;              // Relating x position to x velocity

    der(y)=vy;              // Relating y position to y velocity

    x^2+y^2=L^2;            // Constraining x, y to string length

end Pendulum;

```

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``` OpenModelica

translateModelFMU(Pendulum)

```

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``` OpenModelica

// generates C code and complies an exe

// that produces a result file

buildModel(Pendulum fileNamePrefix="pendulum-")

```

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``` OpenModelica

// builds model & runs it

simulate(Pendulum, fileNamePrefix="pendulum-")

```

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``` OpenModelica

plot(der(x),der(y),m)

```

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``` OpenModelica

// remove artifacts

remove("pendulum-*")

```

%% Cell type:code id: tags:

``` OpenModelica

class Spring "Damped Spring"

    // mass, gravity, spring constant, air, contact resistance

    parameter Real m=0.5, g=9.81, k=3, r_a=0.1, r_c=0.0;

    output Real x(start=0.0);  // x position

    output Real vx(start=0.2); // x velocity

equation

    // 2 variables, 2 equations

    m*der(vx)= -k*x - r_a*vx - r_c*m*g; // force equation

    der(x)=vx;                          // relating position to velocity

end Spring;

```

%% Cell type:code id: tags:

``` OpenModelica

simulate(Spring, fileNamePrefix="spring-*")

```

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``` OpenModelica

plot(der(x), x)

```

%% Cell type:code id: tags:

``` OpenModelica

// remove artifacts

remove("spring-*")

```