Frequently asked questions about Scicos

General questions regarding the Software:

Q: What is Scicos?
A: Scicos is a modeling, simulation and code generation tool for hybrid dynamical systems. In many respects, Scicos is similar to programs such as Matlab/Simulink, SystemBuild and Dymola. Scicos is a ScicosLab toolbox.

Q: Who develops Scicos?
A: Scicos is developed by the Scicos Team under the direction of its creator Ramine Nikoukhah. The Scicos team is part of the Metalau Research Project at INRIA in France. But Scicos, as a free software, also benefits from contributions from all over the world.

Q: Is Scicos free software?
A: Scicos 4.2 and 4.2.1 were distributed under both the Scilab 4 license and GPL in order to be included in both Scilab 4 and Scilab 5. Scicos 4.4 is only made available in ScicosLab, a fork of Scilab 4, so Scicos 4.4 is only distributed under the Scilab 4 license. Under this license, Scicos can be used freely in commercial and non-commercial applications as long as a modified version is not distributed under a different license. See the license.txt file included in the package for more details.

Q: Does Scicos work on my computer?
A: ScicosLab runs on Windows and most Linux and Mac operating systems.

Q: How do I install ScicosLab?
A: Download the latest release of Scilab from http://www.scicoslab.org and visit regularly our web site http://www.scicos.org for unstable releases.

Q: What is the latest version of Scicos?
A: Scicos 4.4 is the latest version. This version is distributed with ScicosLab 4.4.

Q: Is there any documentation available on Scicos?
A: Yes, the software itself is well documented and more information can be found on http://www.scicos.org.

Q: Does Scicos assure backward compatibility?
A: Yes, when loading an old diagram, Scicos translates it into the new format. The incremental translation mechanism allows you to load even very old Scicos diagrams but the translation time can be long. Make sure you save the diagram after translation to avoid having to go through the translation process again.

Q: Can Scicos read diagrams made in other tools such as Dymola or Simulink?
A: No. The current version of Scicos contains a very basic Modelica compiler. This means that only very simple models constructed in Dymola can be read in Scicos. The work is in progress however to develop a full Modelica compiler leading to full compatibility with Dymola and other tools based on Modelica. As for Simulink, even though Scicos can be used to construct most diagrams modeled in Simulink in a very similar fashion, the underlying formalism of Scicos is different. Scicos is inspired by synchronous languages such as Signal and in particular their extension to continuous-time dynamics. It is perceivable to have at some point inter-operability between Scicos and Simulink, but no such a project is currently considered by the Scicos team.

Scicos Editor:

Q: The old Scicos editor had many limitations and its behavior was not similar to other graphical editors. Why was that?
A: For a long time, no work had been done to improve the Scicos editor. But a lot of effort has been put into this editor recently, making the latest version of the Scicos editor comparable to that of similar tools. There are of course some limitations stemming from Scilab graphics limitations and bugs. A simple mouse press for example is not detected immediately in Scilab; a timer is used systematically for detecting potential double-clicks. This slows down a bit the system's response (this problem does not exist on the Scilab GTK version). A number of important events are simply not detected by Scilab, such as window resizing or window iconification. Some events are lost when switching windows and some captured erroneously. Finally some important functionalities such as inhibiting a window closure is not present. We have written a lot of code to (hopefully successfully) circumvent these problems.

Q: Has the stability of the Scicos editor been improved?
A: Yes. All the menu calls are now protected via the usage of Scilab exec functions with 'errcatch' option. Unfortunately these Scilab functions are fragile (bugs reported but not corrected yet), that is why their protection is not 100% effective. To get around this problem, we have added additional layers of protection, which overall should provide a lot of stability. Just beware of the menu "icon_editor". This functionality has not been fully tested and may crash Scilab. If you want to use it, it is recommended to save a copy of your diagram beforehand.

Q: What language is the Scicos editor programmed in?
A: Except for some GUIs written in TCL/TK, the Scicos editor is written entirely in Scilab language. The editor windows are standard Scilab graphical windows and diagrams are drawn using scilab's new graphics library instructions. Using Scilab as a programming language may seem an odd choice however it provides a flexible environment for developing new functionalities in Scicos. The limitations are mainly the absence of structures in the Scilab language (contrary to what its name suggests, a "list" in Scilab is just a record). This slows down the manipulation and in particular the compilation of very large diagrams. However for most applications, this is not an issue.

Q: I have used Scicos in the past. The new editor seems to have changed a great deal in the latest version. Is there anything in particular that I should be aware of?
A: The behavior of the new Scicos editor has pretty much the standard Windows look and feel now. We have tried to keep the old functionalities as much as possible, but there are a few points you should look for.
- In the old editor, to start a link off another link (i.e. to create a split) a simple click on the split point was used. In the new editor a click is used to select an object (in this case the link), to create a split you should double-click on the split point, or as in the old editor, use a keyboard shortcut (the default is "l").
- In the old editor, only one editor window was active at a time. In the new editor, multiple windows containing different subsystems of the model can be simultaneously open and active. However, when copying a block from a palette using drag and drop, the block can only be placed in the subsystem window having the focus. This limitation will be lifted in the future. Note that it can be placed anywhere with the copy and paste operation.
- The Navigator function has been replaced with the Browser.
- The Save As Interfacing function is maintained, however the new editor proposes a more powerful mechanism for creating new Interfacing Functions. See the Masking operation.
- If you run out of space when constructing your model, you can increase the size of the canvas by doing a Replot (default keyboard shortcut is "r"). If you don't want a bigger space but smaller blocks, try ZoomIn (shortcut "-"). And don't forget, you can use hierarchy (Super Blocks) to avoid diagrams with too many blocks.
- You should remove the files .scicos_pal and .scicos_short if they have been created by the old Scicos editor. Scicos will create new ones if needed.

Q: While editing a Scicos diagram, I would like to use Scilab once in a while to do some computations or load a function for use in Scicos. Is this possible?
A: In the old editor the only way to activate Scilab prompt was using the "Calc" menu. This menu activates Scilab shell in the debug level. Scilab computations can be preformed there but the results, along with any loaded functions, would be lost upon returning to Scicos. In the new editor, it is possible to go back and forth between Scilab and Scicos. In Scicos, simply use the "Activate Scilab Window" menu. To return to Scicos, simply click on any Scicos window (or simply type "scicos;" on Scilab prompt). Note that this feature is particularly useful for taking advantage of the "From/To Workspace" blocks.

Q: Is there a way to avoid drawing connection links between blocks; this is particularly cumbersome when a link connects two blocks situated in two distant subsystems?
A: Yes, you can use "From" and "Goto" blocks.

Q: How do I export the picture of a Scicos diagram for inclusion in a Latex or Word document?
A: You can directly export any Scicos diagram in PostScript format, but you can also export it to a standard Scilab graphics window and export it from there in various formats supported by Scilab.

Q: The widget to pick a file for the Open and SaveAs operations under Windows is no longer the standard Windows widget, why? How do I open a file on a device or on another disk?
A: Scilab function xgetfile and tk_savefile crash Scilab under Windows. This happens rarely but if it does, the user would lose his/her Scicos diagram. That is why we have decided to use a less convivial tk widget instead. To switch to a device, say D, simply type in "D:" followed by carriage return.

Q: The keyboard shortcuts do not always function under Xwindow. Why?
A: This is an old Scilab bug: when the Num_lock is engaged, the keyboard events are not captured by Scilab. Disengage the Num_lock or compile Scilab with the gtk2 option.

Scicos Compiler and Formalism:

Q: Has the compiler been improved in Scicos 4.2?
A: Besides being able to handle very general data types (various integer data types, matrices, complex type), the main compiler routine, responsible for the computation of the scheduling tables, has been re-written.

Q: Is it possible to construct a new block in Scicos?
A: Of course. A new block can be a masked sub-model, or can be written completely from scratch in C or in Scilab language. With some limitations, a new block can also be constructed using Modelica language.

Q: I have written many Simulink S-Functions, is it easy to adapt them for use in Scicos?
A: Yes. In most cases an S-Function, with little changes, can be used as the simulation function of a new Scicos block.

Q: Scicos diagrams mix implicit Modelica based blocks with standard explicit C/Scilab based blocks. How does the compiler handle this co-existence?
A: If the model contains implicit (Modelica based) blocks, Scicos puts them together and generates a single Modelica program. The built-in Modelica compiler then generates a C code, which is compiled and linked with Scicos. This code becomes the simulation function of a new Scicos block replacing all the implicit blocks. From there on, the compilation proceeds just as for any standard Scicos diagram. All of these steps are of course completely transparent for the user.

Q: For very large diagrams containing sub-sampling operations, the compilation time can become long. Is there a problem with the algorithm used in the Scicos compiler?
A: The problem is not the algorithm. The algorithm is written for the large part in Scilab. The compilation time can be drastically reduced if the algorithm is coded in C. This will be considered if the compilation time becomes a real issue.

Q: Having explicit control over activation signals in Scicos is a very nice feature for specifying, without ambiguity, the synchronous and asynchronous behaviors of the model. But sometimes, specially when all the discrete-time clocks are synchronous, it is more convenient to just give the frequency and the phase of each clock and let the system take care of synchronization. Is this possible in Scicos?
A: Yes, see SampleClock blocks introduced in Scicos 4.2.

Q: What does the compiler take as input and what does it generate?
A: The Scilab structure "scs_m" contains a full description of the diagram. The compiler takes this structure and generates another Scilab structure "%cpr" that contains the scheduling tables and other information needed by the simulator.

Q: In some situations, the compilation takes a lot less time than others, why?
A: There are different levels of compilation in Scicos. Depending on the type of change made in the diagram, Scicos can initiate a full compilation or choose among different levels of partial recompilation options. Note also that if a diagram is saved in ".cos" format after being compiled, the compilation result "%cpr" is also saved. So upon re_opening, no compilation is needed.

Scicos Simulator:

Q: What numerical solvers are used in Scicos?
A: Up to version 4.2, Scicos has used LSODAR and DASKR. But now it uses the SUNDIALS solvers CVODE and IDA.

Q: Is it possible to interface additional numerical solvers with Scicos simulator?
A: It is possible but it is not easy. The numerical solver must have proper zero-crossing mechanisms. It is not recommended to undertake such a work without collaboration with the Scicos team.

Q: At the end of a simulation, scope contents are erased for a short period of time and redrawn. Why? This was not happening in older versions of Scicos.
A: Since version 4.2, Scicos uses the new Scilab graphics library. At the end of the simulation, the segments drawn during the simulation are replaced with a single polyline for each curve. This way, the curve can conveniently be edited with Scilab's graphical editor.

Q: Is it possible to make the final simulation time depend on a formal parameter (a parameter defined in the context of the diagram)?
A: Yes, you can use the END block (Others Palette). Note that this block is different from the PAUSE block in that END really ends the simulation whereas PAUSE merely stops the simulation, which can subsequently be continued.

Scicos Code Generator:

Q: What is the code generator?
A: The code generator is a Scicos functionality that generates a C code from the content of a Super Block. The C code is used as the simulation function of a new basic block which replaces automatically the Super Block for validating the correctness of the generated code. The necessary supporting files are also generated so that the code can be used as a standalone application. The code generator functions both under Windows and Linux/Unix operating systems.

Q: Can code generation be used for any Super Block?
A: It can for most Super Blocks. The only restriction is that the blocks inside the Super Block should not generate asychronous events. As for continuous-time dynamics, only explicit blocks are allowed and for standalone applications, the generated code contains fixed-step solvers.

Q: Can Scicos generate standalone code for any Super Block?
A: Many restrictions present previous versions have been lifted in Scicos 4.4. It is now possible to generate code for almost any Super Block.

Modelica extension:

Q: When is the Modelica compiler used in Scicos?
A: Scicos does not use Modelica as long as the diagram contains only standard Scicos blocks, i.e., blocks with explicit inputs and outputs. Modelica is used to model implicit blocks used for component based modeling. Such blocks have ports which are not labeled a priori as input or output. They allow in particular the modeling of electrical or mechanical components.

Q: Which Modelica compiler is used in Scicos?
A: modelicac is a free open source compiler developed in the framework of the RNTL Simpa project. This compiler, which covers only very partially the features of the Modelica language, is replaced by a more complete compiler, developed in the Simpa2 project by LMS-Imagine.

Q: I cannot run models with Modelica components, I get an error message about "nmake" not being available. Why?
A: Modelica compiler generates C code that has to be compiled. Under the Windows operating system, you need to have the Visual C++ or the free Visual Express compiler installed on your computer.

Q: I have a Modelica code describing the dynamics of a block, what is the easiest way to use it in Scicos? Can I avoid writing an interfacing function?
A: Yes, you can use the Modelica Generic block in the Others palette.