Microsoft Windows Platforms Impose a Limit on the Number of Distinct Models That Can Be

Microsoft Windows Platform limitation on number of distinct models in a model reference hierarchy

Microsoft Windows platforms impose a limit on the number of distinct models that can be referenced by a parent model. The limit is due to command prompt (cmd.exe) command line string limitation. For details on cmd.exe limitation refer to Microsoft support at

On Windows platforms, simulating referenced models invokes cmd.exe. This is also true when generating code from referenced models. This is because every model is dependant on its referenced model’s code. While compiling the code for a model, each of its dependant referenced model’s code path needs to be included (via –I option). Hence the compile command is concatenated string of include paths.For large model hierarchies, the number of dependent models could be large and hence the length of the compile command string can become very large. When the string length exceeds the limit set by Windows’ cmd.exe, simulation (or code generation) could error out.

The exact number of models, where the error could occur,varies from one model hierarchy to another and is dependant on the following

1)The Windows platform version. On Windows XP, the limit is higher than Windows NT.

2)The length of each referenced model name. For example, if the average model name length is 25 characters, the limits are approximately 40distinct models on Microsoft Windows 2000 and 300 distinct models on Microsoft Windows XP.

3)Whether, the referenced model is configured as One-instance or Multiple-instance.

While the first two factors are easy to understand, the third factor needs a little more explanation. The next section documents how the instance-setting on the model and model partitioning contribute to the problem.

Note: The limit does not apply to multiple instances of the same model. For example, suppose that your model references 50 instances of model A and 75 instances of model B. In this case, models A and B count as only two against the referenced model limit, despite the fact that your model references 125 instances of these two models.

Calculating the number of dependant models in a hierarchy

Using find_mdlrefscommand in MATLAB one can determine the total number of distinct referenced models in a model hierarchy. However, for compiling a model, not every referenced model path needs to be included in the compile command string. For avoiding the cmd.exe, it is necessary to keep the number of dependant models to a low number.

A referenced model could either contribute to the list of dependant models or be independent of the top model. The dependency is decided by

1. The position where it appears in the hierarchy. The referenced models at first level of hierarchy are always counted as dependant models. You can use find_mdlrefs to determine the models at first level. You can use the view_mdlrefs to visualize the entire hierarchy.
2. For each referenced model at the first level, its configuration parameter ‘Total number of instances allowed per top model’ value affects if the models at other levels are counted as dependant models. If the setting is “Multiple”, itself and every model referenced by it is counted as a dependent model for the top model. If the setting is “One”, as stated earlier, only itself is counted as a dependant model
3. The top model’s configuration parameter ‘Total number of instances allowed per top model’ value. Note, this affects only if you are generating code from the top model. This does not affect

Hence, the number of dependant distinct models is bounded. It can be expressed mathematically as

In the following example hierarchy, for mParent model, the number of referenced models at first level is “2”: mTop and mTop_fixstep. There are 4 models at other levels. Using Rules#1 through 3, the number of dependant models would be greater than or equal to 2, but less than or equal to 6.

Per Rule#2, setting the parameter to "Multiple" forces the next level of models to be counted as dependant models. In the following table, the effect of the setting is shown for various settings of models mMid and mMid_fixstep. These models are at the level 2 of the hierarchy

Table 1

Using the same logic, we can extend the table to the next level of models – mTop and mTop_fixstep.

Table 2

Strategies for creating scalable model reference hierarchies

Given, Microsoft Windows limitation, users have to strategize while creating large model hierarchies. For successful simulation and code generation, the best strategy is to keep the number of dependant models to a lowest possible number. Here are some modeling guidelines which can help

1)For referenced models at any level, exercise judgement when setting a referenced model’s configuration parameter ‘Total number of instances allowed per top model’ value. If, and only if, it is being re-used elsewhere then set it to “Multiple”. Otherwise, set it to “One”.

2)For models at first level of hierarchy, try to set the number of instances allowed to “One”. For models at other levels, set “Multiple” instances only if reusable.

3)If the number of models at first level is very large, split the level into two or more levels.