README.md improved

Author: MartinOtter

README.md

@@ -3,16 +3,18 @@
 [![Stable](https://img.shields.io/badge/docs-stable-blue.svg)](https://modiasim.github.io/Modia.jl/stable)
 [![The MIT License](https://img.shields.io/badge/license-MIT-brightgreen.svg?style=flat-square)](https://github.com/ModiaSim/Modia.jl/blob/master/LICENSE)
 
-Modia is part of [ModiaSim](https://modiasim.github.io/docs/).
+The [Modia Tutorial](https://modiasim.github.io/Modia.jl/stable/Tutorial.html) provides an introduction to Modia. Modia is part of [ModiaSim](https://modiasim.github.io/docs/).
 
-The [Modia Tutorial](https://modiasim.github.io/Modia.jl/stable/Tutorial.html) provides an introduction to Modia.
+Modia is a Julia package for modeling and simulation of multidomain engineering systems
+described by differential equations, algebraic equations, and (space-discretized) partial differential equations. It shares many powerful features of the [Modelica language](https://www.modelica.org/modelicalanguage), together with features not available in Modelica. 
 
-Modia is a Julia package for modeling and simulation of multidomain engineering systems (electrical, 3D mechanical, fluid, etc.) described by differential equations, algebraic equations, and (space-discretized) partial differential equations. It shares many powerful features of the
-[Modelica language](https://www.modelica.org/modelicalanguage), together with new features not available in Modelica. 
+A user defines a model on a high level with model components (like an electrical resistance, a rotational inertia, a rod with heat transfer, a PI controller etc.) that are physically connected together. A model component is constructed by "expression = expression" equations. The defined model is symbolically transformed to ODE form dx/dt = f(x,t). For example, equations might be analytically differentiated, ODE states selected, linear equation systems numerically solved when evaluating the function. From the transformed model a Julia function is generated that is used to simulate the model with integrators from [DifferentialEquations](https://github.com/SciML/DifferentialEquations.jl). Simulation results are plotted with [ModiaPlot](https://github.com/ModiaSim/ModiaPlot.jl), providing a convenient interface to [GLMakie](https://github.com/JuliaPlots/GLMakie.jl) line plots.
 
-Simulation is performed with [DifferentialEquations.jl](https://github.com/SciML/DifferentialEquations.jl), units are supported via [Unitful.jl](https://github.com/PainterQubits/Unitful.jl) , uncertainty modeling is performed with [Measurements.jl](https://github.com/JuliaPhysics/Measurements.jl), Monte Carlo simulation is performed with [MonteCarloMeasurements.jl](https://github.com/baggepinnen/MonteCarloMeasurements.jl). 
+Other packages from the Julia eco-systems that are specially supported:
 
-Plotting is performed with package [ModiaPlot.jl](https://github.com/ModiaSim/ModiaPlot.jl) as convenient interface to GLMakie.
+- [Unitful](https://github.com/PainterQubits/Unitful.jl) to define and process physical units.
+- [Measurements](https://github.com/JuliaPhysics/Measurements.jl) to perform simulations with uncertain parameters and initial values with linear propagation theory.
+- [MonteCarloMeasurements](https://github.com/baggepinnen/MonteCarloMeasurements.jl) to perform simulations with uncertain parameters and initial values with particle theory.
 
 
 ## Installation
@@ -26,20 +28,21 @@ julia> ]add Modia, ModiaPlot
 It is recommended to also add the following packages, in order that all tests and examples can be executed in your standard environment:
 
 ```julia
-julia> ]add Measurements, MonteCarloMeasurements, Distributions
+julia> ]add Measurements 
+        add MonteCarloMeasurements
+        add Distributions
+        add Interpolations
 ```
 
-## Example
+## Examples
 
-The following differential equations describes a damped pendulum:
+The following equations describe a damped pendulum:
 
 ![Pendulum-Equations](docs/resources/images/PendulumEquations.png)
 
 
-where *phi* is the rotation angle, *omega* the angular velocity,
-*m* the mass, *L* the rod length, *d* a damping constant,
-*g* the gravity constant and *r* the vector from the origin of the world system
-to the tip of the pendulum. These equations can be defined, simulated and plotted with:
+where *phi* is the rotation angle, *omega* the angular velocity, *m* the mass, *L* the rod length, *d* a damping constant, *g* the gravity constant and *r* the vector from the origin of the world system to the tip of the pendulum. These equations can be defined, simulated and plotted with
+(note, you can define models also without units, or remove units before the model is processed):
 
 ```julia
 using Modia, ModiaPlot
@@ -58,7 +61,6 @@ Pendulum = Model(
    ]
 )
 
-
 pendulum1 = @instantiateModel(Pendulum)
 simulate!(pendulum1, Tsit5(), stopTime = 10.0u"s", log=true)
 plot(pendulum1, [("phi", "w"); "r"], figure = 1)
@@ -68,8 +70,7 @@ The result is the following plot:
 
 ![Pendulum-Figure](docs/resources/images/PendulumFigures.png)
 
-Normally distributed uncertainty can be added, simulated and plotted
-in the following way:
+Simulation and plotting of the pendulum with normally distributed uncertainty added to some parameters is performed in the following way:
 
 ```julia
 using Measurements