Scilab, Another Free Math Alternative

Scilab is matrix oriented math language made freely available for both Linux and Microsoft Windows users. It is not open source, and thus has a few more user restrictions than a purely open source statistics language like R. However the user license is liberal in its allowances.

This web page offers a glimpse into the use of Scilab and compares it to other common matrix languages available in Linux. If you need a definitive guide to using Scilab, check out Engineering and Scientific Computing with Scilab.

At left you see a plot of the sinx/x function as made with the Scilab mesh command. This is the default mesh plot produced by Scilab, without using any of the available enhancements.

Scilab was created and is maintained by INRIA, the French National Institute for Research in Computer Science and Control. By going to scilab.org you can read about Scilab and obtain the latest version. The version I'm reviewing here came packaged with my Etch Debian distribution.

Scilab has a GUI interface even in the Linux version, unlike many of the Linux math languages like Octave, R, and Yorick. The interface is not elaborate, but does give handy access to some file functions and help utilities.

Scilab Syntax

performs the full matrix multiply of x times y. If you wish to only do a cell by cell multiplication of the respective x cells and y cells, a modified multiply operator must be used as in the following example:

The .* operator specifies a scalar operation. The dot modification is also applied to other math operators to indicate a scalar operation preference.

In addition to the matrix data structure, Scilab supports a higher level structure similar to the C-like struct data structure. In this way one can package together different data types under one label. These higher level structures themselves can be kept in arrays, making an array of data structures.

Math operations cannot be performed on these higher level structures, but can be performed on the individual elements of the structure, such as on a matrix that might be one of the elements. For example, you can create an x variable that has more than one conceptual element. In the following case, an x variable is created that has a, b, and c elements. The a element is a 3x3 matrix, the b element is a scalar, and the c element is a 3x2 matrix.

The a portion of the structure can be addressed by x.a, and so on. If y is and array of these structures, the addressing would be z = y(i).a, where i is the desired index of the high level y array.

Scilab is not a clone of MATLAB. It is similar in function and syntax, but certainly not exactly the same. If you're really wanting an alternative that has a closer syntax to MATLAB, then I suggest you consider Octave.

None-the-less, Scilab matrix nomenclature and I/O are quite similar to MATLAB so users could make the transition fairly easily. Logic structures are an example of the nature of the differences between the languages. In Scilab, a simple end statement marks the end of most logic constructs, like for statements and if statements.

One of the main differences is that with Scilab, user function files must be loaded with a getf command before they can be used, rather than auto-loaded on reference as in MATLAB and Octave. It's common to store several functions in a single file, making the file more of a library of functions. Thus a single getf command can load a number of related functions all at once.

Scilab also uses the varargin array method of passing a variable number of arguments to user-defined functions. And as with Octave, some logic must be generated by the user to handle whether function variables have default values, or are passed values embedded in varargin.

Packages and I/O

Scilab has a large collection of engineering oriented packages covering signal processing, linear algebra, filtering, sound file handling, and a number of statistics functions. Scilab comes complete with a pretty handy GUI interface in Linux and in Windows.

Scilab provides simple commands for saving and loading matrices in a Scilab native form. It also has commands for loading and saving MATLAB compatible files. Scilab can even load xls spreadsheet files. Also provided are some primitive I/O commands that give Scilab users the ability to read and write most file formats they might need, providing they have documentation on the formats.

Included with Scilab is a GUI programming utility called scicos. With scicos, one can drag icons of different math functions onto a graphical window, edit them to set parameters or describe functions, connect them into a desired logical sequence, and then initiate the process that will run the graphically designed simulation.

Help is available in Scilab through the GUI as a pull down menu, or one can type help topic and help of the topic will pop up in a window. Once help is initiated, it can be navigated by using the mouse.

Scilab Graphics

Scilab has a very robust integrated graphics package, supporting the making of all manner of line plots, contours, color contours, and surface maps. At left you see a line contour map made by Scilab. The labeling and annotations of the axes can be controlled, the number of contours can be selected, and various other aspects of the presentation can also be controlled. Contours of large matrices are created fairly quickly.

As this image illustrates, Scilab can also be configured to display color filled contours. The user can use the colormap utility to set any desired colormap for presentation. Scilab can also render images, such as a digital camera image. However I was unable to find an image loader for Scilab. Apparently if one wants to load an image into Scilab for processing in some way, the image must be turned into one of the binary or ASCII matrix forms that Scilab can handle.

I used a pdl script to convert an image into a format that Scilab could load. I found that Scilab wasn't very fast at rendering images that were perhaps 300 x 300 or so in size. Scilab can, however, export a graph in a few standard graphics formats. It can export a graph as a GIF file, a postscript (ps) file, or a PPM file.

The image at the right is another mesh, but with an added z-axis correlated color map. User selected or generated color maps are used for both contour and 3D images. Scilab does provide the user the ability to interact with a graph. Commands are available for obtaining the location of the mouse within a graph, and for obtaining mouse button information. One can, for example, use the Scilab rubber band box to select a section of a plot.

Summary