Construction and Simulation of a Simple Model

In this tutorial, we will simulate a very simple model consisting of a generator and a writer as shown in the block diagram shown below.


Model Simulation

Let us construct the model first. See Model Construction for more detailed information about model construction.

using Causal

# Describe the model
@defmodel model begin
    @nodes begin
        gen = SinewaveGenerator()
        writer = Writer()
    @branches begin
        gen => writer

In this simple model, we have a single output sinusoidal wave generator gen and a writer. In the script above, we constructed the components, connected them together and constructed the model.

We can specify simulation settings such as whether a simulation log file is be to constructed, model components are to be saved in a file, etc.

simdir = "/tmp"
logtofile = true
reportsim = true

At this point, the model is ready for simulation.

t0 = 0.     # Start time
dt = 0.01   # Sampling interval
tf = 10.    # Final time
sim = simulate!(model, t0, dt, tf, simdir=simdir, logtofile=logtofile, reportsim=reportsim)
Simulation(state:done, retcode:success, path:/tmp/Simulation-37085bb8-c723-4249-9751-206da508dbc3)

Investigation of Simulation

First, let us observe Simulation instance sim. We start with the directory in which all simulation files are saved.

foreach(println, readlines(`ls -al $(sim.path)`))
total 80
drwxr-xr-x 2 juliateam juliateam  4096 May 10 17:06 .
drwxrwxrwt 1 root      root      28672 May 10 17:06 ..
-rw-r--r-- 1 juliateam juliateam 15332 May 10 17:06 e673eb9e-6814-44e9-8ce5-e140cea88326.jld2
-rw-r--r-- 1 juliateam juliateam 21490 May 10 17:06 report.jld2
-rw-r--r-- 1 juliateam juliateam  1160 May 10 17:06 simlog.log

The simulation directory includes a log file simlog.log which helps the user monitor simulation steps.

# Print the contents of log file
open(joinpath(sim.path, "simlog.log"), "r") do file
    for line in readlines(file)
┌ Info: 2021-05-10T17:06:31.089 Started simulation...
└ @ Causal /juliateam/.julia/packages/Causal/vOCIT/src/utilities/utils.jl:5
┌ Info: 2021-05-10T17:06:31.152 Inspecting model...
└ @ Causal /juliateam/.julia/packages/Causal/vOCIT/src/utilities/utils.jl:5
┌ Info: 2021-05-10T17:06:31.165 Done.
└ @ Causal /juliateam/.julia/packages/Causal/vOCIT/src/utilities/utils.jl:5
┌ Info: 2021-05-10T17:06:31.165 Initializing the model...
└ @ Causal /juliateam/.julia/packages/Causal/vOCIT/src/utilities/utils.jl:5
┌ Info: 2021-05-10T17:06:31.369 Done...
└ @ Causal /juliateam/.julia/packages/Causal/vOCIT/src/utilities/utils.jl:5
┌ Info: 2021-05-10T17:06:31.369 Running the simulation...
└ @ Causal /juliateam/.julia/packages/Causal/vOCIT/src/utilities/utils.jl:5
┌ Info: 2021-05-10T17:06:31.436 Done...
└ @ Causal /juliateam/.julia/packages/Causal/vOCIT/src/utilities/utils.jl:5
┌ Info: 2021-05-10T17:06:31.436 Terminating the simulation...
└ @ Causal /juliateam/.julia/packages/Causal/vOCIT/src/utilities/utils.jl:5
┌ Info: 2021-05-10T17:06:31.453 Done.
└ @ Causal /juliateam/.julia/packages/Causal/vOCIT/src/utilities/utils.jl:5

report.jld2 file, which includes the information about the simulation and model components, can be read back after the simulation.

julia> using FileIO, JLD2

julia> filecontent = load(joinpath(sim.path, "report.jld2"))
Dict{String, Any} with 9 entries:
  "retcode"         => :success
  "name"            => "Simulation-37085bb8-c723-4249-9751-206da508dbc3"
  "model/callbacks" => nothing
  "model/name"      => ""
  "clock"           => Clock(gen:0.0:0.01:10.0, paused:false)
  "model/id"        => "9ebc8cc3-02fb-4037-9cb4-c793276583bc"
  "components/"     => SinewaveGenerator(amp:1.0, freq:1.0, phase:0.0, offset:0…
  "path"            => "/tmp/Simulation-37085bb8-c723-4249-9751-206da508dbc3"
  "state"           => :done

julia> clock = filecontent["model/clock"]
ERROR: KeyError: key "model/clock" not found

Analysis of Simulation Data

After the simulation, the data saved in simulation data files, i.e. in the files of writers, can be read back any offline data analysis can be performed.

# Read the simulation data
t, x = read(getnode(model, :writer).component)

# Plot the data
using Plots
plot(t, x, xlabel="t", ylabel="x", label="")
QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-juliateam'
QPainter::begin: Paint device returned engine == 0, type: 3
QPainter::setCompositionMode: Painter not active
QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1

A Larger Model Simulation

Consider a larger model whose block diagram is given below


The script below illustrates the construction and simulation of this model

using Causal 
using Plots

# Construct the model 
@defmodel model begin 
    @nodes begin 
        gen1 = SinewaveGenerator(frequency=2.)
        gain1 = Gain()
        adder1 = Adder(signs=(+,+))
        gen2 = SinewaveGenerator(frequency=3.)
        adder2 = Adder(signs=(+,+,-))
        gain2 = Gain()
        writer = Writer() 
        gain3 = Gain()
    @branches begin 
        gen1[1]     =>      gain1[1] 
        gain1[1]    =>      adder1[1]
        adder1[1]   =>      adder2[1]
        gen2[1]     =>      adder1[2]
        gen2[1]     =>      adder2[2]
        adder2[1]   =>      gain2[1]
        gain2[1]    =>      writer[1]
        gain2[1]    =>      gain3[1]
        gain3[1]    =>      adder2[3]

# Simulation of the model 
simulate!(model, withbar=false)

# Reading and plotting the simulation data
t, x = read(getnode(model, :writer).component)
plot(t, x)
savefig("larger_model_plot.svg"); nothing # hide