MLDesign Technologies, Inc.






Frequently Asked Questions

Find answers to MLDesigner-related questions

This chapter is designed to help you find quick and short answers to your questions. All these topics are covered in detail in the MLDesigner user manual which can be opened by clicking the Help button in the top right corner of the GUI and selecting the option Search Index.

1.1 General Questions

  1. Do I need to learn Ptolemy and BONeS to be able to design with MLDesigner?
  • No but it is necessary to bear in mind that the Ptolemy base type int is different to any data structure type including those like Root.Integer. It is only possible to connect ports of the same type.

1.2 Error Messages and Their Most Common Causes

  1. Cannot create library ”xxx” to location ”file:/user/xxx/yyy/zzz/xxx.mml”. Maybe you have no write permission. Cannot create model ”xxx”. You must create the library ”yyy” first.
    • No but it is necessary to bear in mind that the Ptolemy base type int is different to any data structure type including those like Root.Integer. It is only possible to connect ports of the same type.
  2. Compilation error , unable to load the primitive Dynamic.
    • Firstly your primitive contains syntactical errors and can not be compiled by the C++ compiler. In that case you will get an error dialog (”Compilation failed.”), when you compile the primitive in MLD. You should open the primitive editor, try to compile it and correct the reported errors until successful compilation is confirmed.
    • Secondly a primitive with the same name already exists in the same Domain.
    • Another reason could be the primitive was already loaded with Load mode set to Per- manent. If a Primitive is loaded permanent it is not possible to make any changes to its source code and then recompile the primitive. You must shutdown MLDesigner and restart before the changes take effect. You only need to load a primitive as permanent if you want it to be inherited by another primitive. A primitive that is a child of another primitive can only be recompiled if the parent is loaded as permanent.
  3. ”make: fatal error in reader: /export/home/mldesigner/mk/,line 59: Unexpected end of line seen”.
    • This error is often caused by compiler incompatibility. What version of make do you use? You need gmake 3.74 or later. Please look at the section on system requirements.

1.3 Segmentation Faults

  1. What are the most common causes of segmentation faults that cause MLDesigner to crash?
    • The most common reason for system crashes with MLDesigner is programmer error in user defined primitives. When a segmentation fault occurs you should first check to see if your system contains user defined primitives. Often the crash is caused by inconsistencies in memory allocated to output datasets. The next step is to run the simulation extern possibly using an external debugger to debug the system. External simulations occur outside of the MLDesigner environment. See the MLDesigner documentation for more information on debugging.

1.4 Data Structures

  1. When must a data structure be deleted and when is it a clone?
    • When to clone a particle: Generally you don’t have to clone particles. In sending particles over the ports you can use operators like << or =. For data structures the situation is more complicated, because you have to take into account how it is instantiated as a data structure and how it is used.
    • When to create a new particle: When you instantiate a new data structure for direct usage (not to be used as parameter in a method that takes const Type * as parameter - methods of setType() kind), you have to use the method DsHandler::makeNewStructure().
    • When is a particle a clone? When you set a data structure to a Memory, Event or a DataStructMember, the parameter is cloned inside the method so there is no need for a new created object.
    • When to delete a data structure: When you get a data structure using the method DsHandler::makeNewStructure() be sure to delete it to avoid overloading memory. Every new data structure created using the clone () method must be deleted. The exception is when you place it on an output port. DataStructParticles take care to delete the data structure when the last reference to it is deleted. Do not delete const pointers to Type or class derivedfrom, returned by some methods. These are references to the class members and the object takes care of deleting them. On the contrary, non const pointers to Types must be deleted if you are not in the exceptional case previously mentioned.
    • Do not delete particles when: As an exception, don’t delete the non const Type * returned by DataStructMember’s methods getData () or fieldWithName () of the DataStructureclass, or every time when you write or read a Memory, using writeMemory()
  2. What is a memory leak?
    • A Memory Leak occurs when new memory is allocated dynamically and never deallocated. In C++ new memory is created by the new operator and deallocated by the delete or the delete []operator. Memory leaks accumulate over time and can crash the program.

1.5 Load Mode

  1. What is the difference between Load Mode Dynamic and Load Mode Permanent?
    • While creating a new primitive model component, you can define its load mode. By selecting the load mode Dynamic, a shared library containing the primitive code is created on loading. This shared library is linked dynamically to MLDesigner so that you can reload the primitive any time. All changes made to the primitive are effective immediately. Conversely, by selecting load mode Permanent, the primitive is linked to MLDesigner on loading as it would be with a built-in primitive. All changes made to a primitive with load mode permanent only take effect after closing and restarting MLDesigner.

1.6 Plotting Systems

  1. How do I make data available to, or save data for analysis using external programs?
    • There are a number of ways to display or handle datasets and results of simulations. You may use SatLab to display data. (see Demos/DopplerIR, you need to start SatLab before running the demo!). It uses a Tcl-script $MLD/MLD Libraries/DE/Contrib/WiNeS.tcl.
    • You may save your data to one or more files and postprocess/display it with another tool of your choice. You could for example use a DEPrinter primitive to dump data to a file, then use GnuPlot, Matlab or even a spreadsheet program like StarCalc (within StarOffice) to display the information.

1.7 Setting Environment Variables

  1. How do I change the environment variables so I can use another Editor to debug or change source code in my primitives?
    • To define the editor you prefer to use when working with source code it is no longer necessary to set the environment variables. A dialog is available where a variety of setting can be changed. To define which editor you prefer click the Settings option in the main menu. Expand the tree by clicking the Primitive Source Editor item. The following options are available:
      • Use external editors with xterm. Some editors open in a terminal and others not. Often the terminal is not required and only gets in the way. To stop the xterm from opening with your editor, click the check box to remove the tick. If the editor cannot open without a console, you will get an error message in the MLDesigner console when attempting to open a source file. In this case make sure you have a tick in the check box. Try open vi without a tick in this check box or set the editor variable to emacs in the $EDITOR input field.
      • Internal. This points to the built-in editor installed with MLDesigner.
      • $EDITOR This radio button sets the default editor to the one you have defined by setting your environment variable. i.e., For sh and bash command shells: export EDITOR=emacs For csh and tcsh command shells: setenv EDITOR=emacs You must close and restart MLDesigner before changes take effect.
      • User-defined Has the same effect as the $EDITOR radio button except you do not have to  close and reopen MLDesigner to get the new setting to work. You must only change the editor name. The @$ are variables that instruct the editor you choose to open the source code of the open primitive in your Model Editor Window.
      • NOTE: The built-in editor is used as default editor in cases where compile errors occur. The reason is that you can highlight errors in the built-in editor error console and the cursor will be automatically placed in the correct line of the source code editor.
  2. How do I change the MLD USER environment variable.
    • It is possible to set your MLD USER environment variable to point to a project library or external library. Lets assume you want to work on a project called MLD.project. This project is the $MLD USER directory of another user. You want to access the systems and share libraries that exist in the other user’s environment. Enter the following command where you would normally open MLDesigner:
      • for bash or sh shells export MLD_USER=/home/user/MLD.project
      • for tcsh and csh shells setenv MLD_USER /home/user/MLD.project
    • You could also do the same locally on your own computer if you wanted to separate libraries and projects. You can create a new directory /MLDProject in your home directory. Set your MLD USER environment variable to point to the new directory. When you open MLDesigner again you will see the tree view with MLDesigner libraries and no user libraries. You could then create a top level library with read and write rights for a workgroup on your network.
  3. How do I change the environment variables so I can use an external debugger?
    • Depending on the type of shell you are using, enter one of the following at the prompt: export MLD_PREBIN=ddd (sh and bash) or setenv MLD_PREBIN ddd (csh and tcsh). The ddd entry refers to the ddd debugger supplied with every Linux package and can be replaced with a call referring to your favorite debugger. You must now start MLDesigner as normal. The debugger you have chosen will start. If you are using ddd proceed as follows:
      • Click the View menu and choose Command Tool.
      • Click Run to start MLDesigner . This can take longer than normal.
      • You can now work as normal with MLDesigner .
  4. Is setting the Working Directory entry the same as setting the $MLD USER environment variable?
    • $MLD_USER and WorkingDirectory are not related to each other at all. The variable $MLD_USER defines where MLDesigner looks for user defined models and libraries where the option WorkingDirectory defines which directory is the working directory for the command console window after starting MLDesigner. Both these topics are explained in the MLDesigner manual which can be opened by clicking on the Search Index option of the Help menu found in the top right corner of the GUI. Find the index entries Command Console or Working Directory to get more detail on the topic.

1.8 ddd debugger and Red Hat

  1. I am running MLDesigner under Red Hat and I am unable to debug using the standard debugger ddd.
    • It is not possible to debug MLDesigner using ddd because Red Hat was developed completely using GCC 2.96 contrary to the recommendations of the Free Software Foundation (see
    • As a result ddd compiled under GCC 2.96 needs a symbol dynamic cast 2 defined in
    • With a SuSE system compiled using GCC 2.95 running under Red Hat, the system crashes when accessing the system internal This is apparently caused by a change in the library interface.
    • At the moment there are no solutions to the problem and we can only suggest you to use gdb or xxgdb as an alternative debugger.

1.9 Linked Objects

  1. Why must I restart MLDesigner before changes made to Linked Object take effect?
    • Files containing object code must be loaded before the primitive that calls the external functions in the object file is compiled. All changes made to the external library will only be actualized when MLDesigner is shutdown and restarted. The reason is that it is not possible to delete the relevant primitive from memory without conflicts arising in the kernel’s reload mechanism. The result would be a primitive containing a mixture of new and old code.

1.10 Shared Libraries

  1. What is the environment variable MLD_SHARED used for and how do I set this variable? Why are there invalid modules in my Shared Libraries?
    • The Shared Libraries directory was introduced to make it easier for design teams to exchange models and work on group projects. It is possible to develop a library within the environment specified byt he $MLD_USER environment variable and then move this library to the shared environment specified by the $MLD_SHARED environment variable. However, since the $MLD_USER variable is dynamic (because it can be different for every user) the following prerequisite applies.
      • All modules and files needed by systems in the library must be located within this library, or in a location that never changes, such as the directory to which $MLD_SHARED and $MLD point.
    • The reason for this is that the systemName.mml file contains references to all model elements needed for the system to function. If these variables change then MLDesigner will not be able to locate the missing model elements.