Save the Model

Step 5 of 5 in Build and Edit a Model Interactively

You can tell that a model has unsaved changes by looking at the title bar in the Simulink^® Editor. An asterisk (also known as the dirty flag) appears in the title bar when a model has unsaved changes..

To determine programmatically whether a model has unsaved changes, you can query the value of the model parameter Dirty with the get_param function. For example, this command saves the current system (gcs) if it is dirty:

if strcmp(get_param(gcs,'Dirty'),'on')
	save_system;
end

Save a Model

To save a model for the first time, in the Simulink Editor, on the Simulation tab, click Save. Provide a location and name for the model file. To see the naming requirements, see Model Names.

To save a previously saved model, follow one of these processes:

To save the model using the current file name, in the Simulink Editor, on the Simulation tab, click Save.
To save the contents of the top model to a new name or location, or to change the model format, in the Simulink Editor, on the Simulation tab, select Save > Save As.
Note
For details about the SLX format, see Upgrade Models to SLX.
To save the contents of a referenced model to a new name, location, or format, open the referenced model as a top model. Then, on the Simulation tab, select Save > Save As.
To save the top model in a format compatible with an earlier Simulink version, on the Simulation tab, select Save > Previous Version. See Export Model to Previous Simulink Version.

Model Names

Model file names must start with a letter and can contain letters, numbers, and underscores. The file name must not be:

A language keyword (e.g., if, for, end)
A reserved name: 'simulink', 'sl', 'sf'
A MATLAB^® software command

The total number of characters in the model name must not be greater than a certain maximum, usually 63 characters. To find the maximum file name length for your system, use the MATLAB namelengthmax command.

To understand how MATLAB determines which function to call when you specify a model name, see Function Precedence Order.

How Simulink Saves Models

When you save a model, Simulink saves the block diagram, block properties, and other information associated with the model in the model file.

If you have any pre-save or post-save callbacks, they execute in this order:

All block PreSaveFcn callback routines execute, then the model PreSaveFcn callback routine executes.
Simulink writes the model file.
All block PostSaveFcn callback routines execute, then the model PostSaveFcn executes.

During the save process, Simulink maintains a temporary backup copy (named modelname.bak) that it uses to restore the model in case of an error. If an error occurs during saving or during any callback during the save process, Simulink:

Restores the original file
Writes any content saved before the error occurred in a file named modelname.err
Issues an error message

When saving a model loaded from an SLX file, the original SLX file must still be present. Simulink performs incremental loading and saving of SLX files, so if the original file is missing at save-time, Simulink warns that it cannot fully reconstruct the file.

Save Models in the SLX File Format

Save New Models as SLX

Simulink saves new models and libraries in the SLX format by default, with file extension .slx. The SLX format is a compressed package that conforms to the Open Packaging Conventions (OPC) interoperability standard. The SLX format stores model information using Unicode^® UTF-8 in XML and other international formats. Saving Simulink models in the SLX format:

Typically reduces file size compared to MDL files. The file size reduction between MDL and SLX varies depending on the model.
Solves some problems in previous releases with loading and saving MDL files containing Korean and Chinese characters.
Enables incremental loading and saving. Simulink optimizes performance and memory usage by loading only required parts of the model and saving only modified parts of the model.

You can specify your file format for saving new models and libraries with the Simulink preference File format for new models and libraries.

Upgrade Models to SLX

If you upgrade an MDL file to the SLX file format, the file contains the same information as the MDL file. Functions that works with MDL files, such as get_param and set_param, also work with the SLX file format. If you upgrade an MDL file to the SLX file format without changing the model name or location, then Simulink creates a backup file by renaming the MDL file (if the file is writable).

If you save an existing MDL file by clicking Save on the Simulation tab, Simulink saves your model in MDL format.

To save an existing MDL file in the SLX file format:

On the Simulation tab, select Save > Save As.
Leave the default Save as type as SLX, and click Save.
Simulink saves your model in SLX format and creates a backup file by renaming the MDL file (if the file is writable) to mymodel.mdl.releasename, e.g., mymodel.mdl.R2010b.

Alternatively, use save_system:

save_system mymodel mymodel.slx

This command creates mymodel.slx, and if the existing file mymodel.mdl is writable, it is renamed mymodel.mdl.releasename.

SLX files take precedence over MDL files, so if both exist with the same name and you do not specify a file extension, you load the SLX file.

Simulink projects can help you migrate files to the SLX format. For an example, see Convert from MDL to SLX in a Project and Preserve Revision History.

Caution

If you use third-party source control tools, register the model file extension .slx as a binary file format. If you do not, these third-party tools might corrupt SLX files when you submit them.

The following table describes operations with possible compatibility considerations when using SLX files.

Operations with Possible Compatibility Considerations when Using SLX What Happens Action

Operations with Possible Compatibility Considerations when Using SLX	What Happens	Action
Hard-coded references to file names with the extension `.mdl`	Scripts cannot find or process models saved with the new file extension, `.slx`.	Make your code work with both the `.mdl` and `.slx` extension. Use functions like `which` and `what` instead of file names.
Third-party source control tools that assume a text format by default	The binary format of SLX files can cause third-party tools to corrupt the files when you submit them.	Register the `.slx` and `.mdl` extensions as binary file formats with third-party source control tools. See Register Model Files with Source Control Tools.
Changing character encoding	Some cases are improved, e.g., SLX solves some problems in previous releases with loading and saving MDL files containing Korean and Chinese characters. However, sharing models between different locales remains problematic.	See SLX Files and Character Encodings.

Hard-coded references to file names with the extension .mdl

Scripts cannot find or process models saved with the new file extension, .slx.

Make your code work with both the .mdl and .slx extension.

Use functions like which and what instead of file names.

Third-party source control tools that assume a text format by default The binary format of SLX files can cause third-party tools to corrupt the files when you submit them. Register the .slx and .mdl extensions as binary file formats with third-party source control tools. See Register Model Files with Source Control Tools.

Changing character encoding Some cases are improved, e.g., SLX solves some problems in previous releases with loading and saving MDL files containing Korean and Chinese characters. However, sharing models between different locales remains problematic. See SLX Files and Character Encodings.

The format of content within MDL and SLX files is subject to change. To operate on model data, use documented functions (such as get_param, find_system, and Simulink.MDLInfo).

Save Models That Have Different Character Encodings

MDL Files and Character Encodings

When you save a model as an MDL file, the current Simulink character encoding encodes the text stored in the model file. This behavior can lead to data corruption if the model contains characters that are not representable in the current encoding. If this is the case, the model is saved as model.mdl.err, where model is the model name, leaving the original model file unchanged. Simulink also displays an error message that specifies the line and column number of the first character that cannot be represented.

To fix this issue, either:

Save the model in SLX format (see Save Models in the SLX File Format).
Change the current Simulink encoding to UTF-8 by using the slCharacterEncoding function and resave the model as an MDL file.

SLX Files and Character Encodings

Saving Simulink models in the SLX format typically reduces file size and eliminates character encoding issues because models are saved using UTF-8 encoding.

You might want to convert your MDL file to an SLX file if you:

Load and save models that have Korean or Chinese characters.
Might benefit from a compressed model file.

Export Model to Previous Simulink Version

You can export a model created with the latest version of the Simulink software in a format used by an earlier version. For example, you can share a model with colleagues who only have access to a previous version of Simulink.

To export a model in an earlier format:

In the Simulink Editor, on the Simulation tab, click Save. This saves a copy in the latest version of Simulink. This step avoids compatibility problems.
In the Simulink Editor, on the Simulation tab, select Save > Previous Version.
In the Export to Previous Version dialog box, from the Save as type list, select the previous version to which to export the model. The list supports seven years of previous releases.
Click Save.

When you export a model to a format of a previous version, the model is saved in the earlier format, regardless of whether the model contains blocks and features that were introduced after that version. If the model contains blocks or uses features that postdate the earlier version, the model might not give correct results when you run it in the earlier version of Simulink software. In addition, Simulink converts blocks that postdate an earlier version into yellow, empty, masked Subsystem blocks. For example, if you use save_system to export a model to Release R2007b, and the model contains Polynomial blocks, Simulink converts the Polynomial blocks into yellow, empty, masked Subsystem blocks. Simulink also removes any unsupported functionality from the model. See save_system.

Save from Earlier Simulink Version to Another Earlier Version

You can open a model created in an earlier version of Simulink and export that model to a different earlier version. To prevent compatibility problems, use the following procedure:

Use the current version of Simulink to open the model created with the earlier version.
Before you make any changes, save the model in the current version by clicking Save on the Simulation tab.
After saving the model in the current version, you can change and resave it as needed.
Save the model in the earlier version of Simulink. On the Simulation tab, select Save > Previous Version.
Start the earlier Simulink version and use it to open the model that you exported to that earlier version.
Save the model in the earlier version.

You can now use the model in the earlier version of Simulink exactly as you could if it had been created in that version.

These Simulink preferences can help you work with models from earlier versions: