Modelica Standard Library

The workbench ships with the Modelica Standard Library 4.1.0: Modelica, ModelicaServices and Complex appear in the package browser next to the bundled Diokle library, with nothing to install. On the command line, pass an MSL checkout as extra sources (see Command line).

In plain terms: the Modelica Standard Library is the common collection of ready-made model parts, and its examples come with reference results, the official answers published by the Modelica Association. An example "matches" when Diokle gives the same answers.

#Coverage

532 of the 534 MSL 4.1.0 example models run to the end, and 513 of the 534 match the Modelica Association's reference results (see below). Seven more run but are documented exceptions: their reference results look wrong, not the simulation (see Reference exceptions). They include:

• Mechanics (Rotational, Translational, MultiBody), Electrical (Analog, Digital, Machines, QuasiStatic machines, PowerConverters, Batteries), Thermal, Blocks, StateGraph and clocked synchronous models;
• Modelica.Media: IF97 water, R134a, ideal-gas mixtures, moist air and reference air, through compiled run-time functions with exact partial derivatives;
• most Modelica.Fluid systems;
• ModelicaStandardTables lookups, replaced by native tables with linear, constant, Akima and Fritsch–Butland smoothness, hold, linear and periodic extrapolation, and time events at breakpoints.

The remaining failures, and what is being done about them, are listed in the Roadmap.

#Reference exceptions

These seven examples run to the end but differ from the reference results, and the evidence says the reference is off. They are not counted as matches, and they are not tolerance changes: the comparison stays at the reference's own tolerance.

• Fluid.Examples.AST_BatchPlant.Test.TankWithEmptyingPipe1: the reference is about 34 tube widths from the exact closed-form solution, while Diokle matches it.
• Fluid.Examples.AST_BatchPlant.Test.TanksWithEmptyingPipe1: the reference is about 3.8 tube widths from Diokle's converged solution.
• Fluid.Examples.AST_BatchPlant.Test.TwoTanks
• Electrical.Analog.Examples.Lines.CompareLineTrunks: OpenModelica 1.27.1 agrees with Diokle on the travelling-wave front at 716.3 µs, so the reference is the outlier.
• Magnetic.QuasiStatic.FundamentalWave IMC_YD and IMC_Transformer: the reference holds rounding noise about 2e-8 where the analytic zero-sequence current is 0.
• Blocks.Examples.DemoSignalCharacteristic: the reference is offset by about 1.5e-4 from the analytic settled values.

#Language features

Each row says what the compiler accepts and where it stops. The numbers count the MSL examples of the matching package that match the reference results (the table in Checked against the reference results has the full breakdown). A feature can be fully supported in the simulator and still be missing from the embedded or CasADi backends, so the last column lists those limits.

The seven StateGraph examples (a block library built from ordinary equations and events, in Modelica.StateGraph) match the reference, but they do not exercise the chapter 17 operators.

Features with no row, such as expandable connectors and homotopy(), have not been measured against the MSL yet, so this table does not claim them.

#External C functions and lookup tables

Many MSL models call C functions from the MSL's own C libraries. Diokle implements these natively, following the reference C sources, so the same models run in the browser:

• ModelicaRandom: the xorshift64*, xorshift128+ and xorshift1024* generators, the impure random generator and automatic seeds, behind Modelica.Math.Random and the Blocks.Noise sources;
• ModelicaFFT: the real FFT behind Modelica.Math.FastFourierTransform;
• ModelicaIO: reading and writing real matrices in MATLAB v4, v6 and v7 files;
• ModelicaInternal and ModelicaStrings: printing, files, time and string functions used by Modelica.Utilities.

The browser bundle holds the .mo sources. The library's Resources/Data files (tables and MATLAB files) are not in it: the site serves them next to the bundle, and the page fetches each one the first time a model reads it, so Utilities.Examples.ReadRealMatrixFromFile can read its .mat files in the browser too (see How the browser loads it).

Functions with constant arguments are evaluated once at translation. Functions with hidden state, such as the impure random generator, are never folded or cached.

Lookup tables follow the C tables exactly:

• CombiTable1D and CombiTimeTable with every smoothness kind of the C tables, first and second derivatives, and the C time-event intervals;
• CombiTable2D with bilinear, constant and bivariate Akima interpolation;
• tables read from text, CSV and MATLAB v4, v6 and v7 files.

Tables supplied through a usertab C function and MATLAB v7.3 (HDF5) files are not supported. These additions made 21 more examples match their reference results:

• all Blocks.Examples.Noise models;
• the FFT examples, Rectifier6pulseFFT and Rectifier12pulseFFT;
• Math.Random.Examples.GenerateRandomNumbers;
• Utilities.Examples.ReadRealMatrixFromFile and WriteRealMatrixToFile;
• the excited synchronous machines (SMEE_*) and RollingWheelSetPulling, after a state-selection fix.

Open the uniform noise example

The state machines of chapter 17 are covered in State machines.

#Checked against the reference results

Simulating is not enough: the results have to be right. A nightly CI job simulates every MSL 4.1.0 example and compares its comparison signals with the Modelica Association's reference results (MAP-LIB_ReferenceResults, generated with Dymola), and fails if a model that passed in the committed baseline stops passing. Each example runs with the tolerance its reference was generated with (the experiment tolerance times 0.1, as recorded in the reference's creation.txt), on the reference's output grid.

The scoreboard lists every example with its status, the signals that differ and the error text, with a link to open it in the workbench.

The baseline is docs/conformance/msl-4.1.0.json, made by tools/refcompare.py.

#Reference results that look wrong

Seven examples do not match, and the evidence says the Modelica Association reference is off, not Diokle. Their closed-form or converged solutions are given in the dispute notes in docs/conformance/reference-disputes.md. They are recorded as documented exceptions and are not counted as matches. No tolerance was loosened to force a match.

• Fluid: AST_BatchPlant.Test.TankWithEmptyingPipe1, TanksWithEmptyingPipe1, TwoTanks
• Electrical: Analog.Examples.Lines.CompareLineTrunks (OpenModelica agrees with Diokle)
• Magnetic: IMC_YD and IMC_Transformer (rounding noise in the zero-sequence current)
• Blocks: DemoSignalCharacteristic

Not exceptions, still open: Fluid.Examples.ControlledTankSystem.ControlledTanks (its tolerance explanation did not reproduce) and Fluid.Examples.TraceSubstances.RoomCO2, whose remaining miss is Diokle's own accuracy at the harness tolerance.

#Examples to try

Each link opens the model in the workbench; press ▶ Simulate.

#Rotational mechanics: CoupledClutches

Four inertias coupled by three clutches that open and close at set times: a classic test of friction events, stuck and sliding phases.

Open Modelica.Mechanics.Rotational.Examples.CoupledClutches

#Analog electronics: ChuaCircuit

A chaotic oscillator. The second subplot plots C2.v against C1.v to show the double scroll attractor.

Open Modelica.Electrical.Analog.Examples.ChuaCircuit

#Control: PID_Controller

A drive train under a PI speed controller, following a kinematic reference profile while a load step hits it.

Open Modelica.Blocks.Examples.PID_Controller

#Heat transfer: TwoMasses

Two masses at different temperatures that equalize through a thermal conductor.

Open Modelica.Thermal.HeatTransfer.Examples.TwoMasses

#MultiBody: DoublePendulum

Two bodies on revolute joints, with the 3-D animation that every MultiBody result gets.

Open Modelica.Mechanics.MultiBody.Examples.Elementary.DoublePendulum

For full vehicle models built on MultiBody, see Multibody vehicles.

#How the browser loads it

The MSL sources are not in the repository. At build time, web/scripts/fetch-msl.mjs downloads the v4.1.0 release from GitHub and packs its .mo and package.order files into one gzip bundle (about 2.6 MB; 14.8 MB unpacked) with a content hash in its name. The workbench downloads it after the Diokle library, unpacks it with DecompressionStream, and registers every file without parsing it. A light token scan outlines each file so the package browser lists the whole library within seconds, and a class is parsed only when it is opened, checked or simulated, together with the classes it needs.

The same script copies the library's Resources/Data files unchanged to public/msl/data/, where the site serves them. They are not part of the bundle, so they cost nothing at start-up. When a translation or a run reads one, for example through Modelica.Utilities.Files.loadResource and then ModelicaIO_readRealMatrix, the file system of the browser asks the page for it. The page fetches it from msl/data/ once and keeps it for the session. A file that the site does not have is reported as not found, as on the command line without the library.