Ecos

Ecos is a co-simulation engine.

Ecos (Easy co-simulation) is a fast, efficient and very easy to use co-simulation engine written in modern C++.

Ecos provides the following features:

• FMI for Co-simulation version 1.0, 2.0 & 3.0.
• SSP version 1.0.
• Optional per process/remote model execution.
• Post-simulation plotting using matplotlib.
• Command-line-interface (CLI).
• Simplified Python and C interface.
• Simple build process (simply build with CMake or pip install).
• Minimal (and bundled) build depedencies.

Building

Ecos bundles all required dependencies. Just build.

//windows
cmake . -A x64 -B build -DECOS_BUILD_EXAMPLES=ON -DECOS_BUILD_TESTS=ON -DCMAKE_BUILD_TYPE=Release
cmake --build build --config Release

//linux
cmake . -B build -DECOS_BUILD_EXAMPLES=ON -DECOS_BUILD_TESTS=ON -DCMAKE_BUILD_TYPE=Release
cmake --build build

Per process / remote execution

Ecos enables models to run on separate processes, possibly on another PC. Simply prepend proxyfmu://localhost?file= to the path of the fmu(s) you load. This is effectively achieved using simplesocket in conjunction with flexbuffers. Just make sure that the proxyfmu target built by libecos is on PATH.

Example

using namespace ecos;

int main() {
    
    simulation_structure ss;

    // add models
    ss.add_model("chassis", "chassis.fmu");
    ss.add_model("ground", "ground.fmu");
    ss.add_model("wheel", "wheel.fmu");
    
    //make connections
    ss.make_connection<double>("chassis::p.e", "wheel.p1::e");
    ss.make_connection<double>("wheel::p1.f", "chassis.p::f");
    ss.make_connection<double>("wheel::p.e", "ground.p::e");
    ss.make_connection<double>("ground::p.f", "wheel.p::f");
    
    // setup initialValues
    std::map<variable_identifier, scalar_value> map;
    map["chassis::C.mChassis"] = 4000.0;
    ss.add_parameter_set("initialValues", map);
    
    auto sim = ss.load(std::make_unique<fixed_step_algorithm>(1.0 / 100), "initialValues");
    
    sim->init();
    sim->step_until(10);
    
    sim->terminate();
}

SSP example

using namespace ecos;

int main() {
    
    auto ss = load_ssp("quarter-truck.ssp");

    // use a fixed-step algorithm and apply parameterset from SSP file
    auto sim = ss->load(std::make_unique<fixed_step_algorithm>(1.0 / 100), "initialValues");
    
    // setup csv logging
    csv_config config;
    config.register_variable("chassis::zChassis"); // logs a single variable
    
    auto csvWriter = std::make_unique<csv_writer>("data.csv", config);
    csvWriter->enable_plotting("ChartConfig.xml"); // enable post-simulation plotting
    sim->add_listener(std::move(csvWriter));
    
    sim->init();
    sim->step_until(10);
    
    sim->terminate();
}

Command line interface

Options:
  -h [ --help ]                 Print this help message and quits.
  -v [ --version ]              Print program version.
  -i [ --interactive ]          Make execution interactive.
  -l [ --logLevel ] arg (=info) Specify log level [trace,debug,info,warn,err,of
                                f].
  --path arg                    Location of the fmu/ssp to simulate.
  --stopTime arg (=1)           Simulation end.
  --startTime arg (=0)          Simulation start.
  --stepSize arg                Simulation stepSize.
  --rtf arg (=-1)               Target real time factor (non-positive number ->
                                inf).
  --noLog                       Disable CSV logging.
  --noParallel                  Run single-threaded.
  --logConfig arg               Path to logging configuration.
  --chartConfig arg             Path to chart configuration.
  --scenarioConfig arg          Path to scenario configuration.

Python interface

To use the python interface, simply clone the project and run:

pip install ./ecospy

Note: You will need wheel in addition to the compile-time requirements listed further below

Example

print(f"Ecoslib version: {EcosLib.version()}")

EcosLib.set_log_level("debug")

fmu_path = "BouncingBall.fmu"
result_file = f"results/bouncing_ball.csv"

ss = EcosSimulationStructure()
if not ss.add_model("ball", fmu_path):
    raise Exception(EcosLib.get_last_error())

with(EcosSimulation(structure=ss, step_size=1/100)) as sim:

    sim.add_csv_writer(result_file)
    sim.init()
    sim.step_until(10)
    sim.terminate()

config = TimeSeriesConfig(
    title="BouncingBall",
    y_label="Height[m]",
    identifiers=["ball::h"])
plotter = Plotter(result_file, config)
plotter.show()

Note: if using an old pip version, append --use-feature=in-tree-build if you get an error about ../version.txt

---

Compile-time requirements

• Windows (10 >=) or Ubuntu (20.04 >=)
• C++20 compiler (MSVC >= 17 || gcc11 >=)
• CMake >= 3.19

Additional Linux requirements

sudo apt install libtbb-dev unzip

Run-time requirements

• Python3 (optional, required for plotting)
  • matplotlib
  • pandas

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Want to build FMUs in C++? Check out FMU4cpp
Want to build FMUs in Kotlin/Java? Check out FMU4j
Want to build FMUs in Python? Check out PythonFMU
SSP generation made easy? Check out SSPgen