Implement representation of symbolic expressions in MATLAB syntax

[swinkler]

Added first version of MATLAB exporter in r5017. Improved GUI of symbolic expression view in r5018.

[gkronber]

Please adhere to our development guidelines.

[...]

• Casing:
  • Classes, interfaces, properties, and methods start with an uppercase letter (e.g. Sheep, Weight, LookABitSilly).
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[gkronber]

Adapted complex program code in MATLAB exporter and reformatted code to adhere to HL coding guidelines with r5019.

[gkronber]

ad r5019: if you don't want duplicates, append .Distinct() to the LINQ statement.

[swinkler]

Thanks for improving the variable names retrieval; updated variable names selection in r5020.

[swinkler]

Corrected evaluation of logical expressions in r5021.

[swinkler]

Tower Dataset (MATLAB data file)

[swinkler]

Script for evaluating MATLAB representations of formulas on the Tower dataset.

[swinkler]

I have tested MATLAB representations of several formulas including arithmetical as well as logical functions on the Tower dataset; in general, the conversion seems to work properly, the estimated values are equal in HL and in MATLAB. Of course, this still needs more testing and review.

I have identified the following problem: The use of the logarithm function is not straight forward. In HL, Math.Log is used and for a nonpositive number this function returns n.def.; in MATLAB, the log of a negative number is a complex number. If the logarithm of a negative number is the condition of a IF node, then we interpret this as false in HL (because (n.def.>0)==false), and in MATLAB the interpretation is true (because a complex number is not equal to 0). We would therefore have to check if the argument is positive or not. I have not yet found a way to solve this, since I have not (yet) found something like the "?" operator we know from C++/C#, e.g.

[gkronber]

A quick google search revealed that indeed MATLAB doesn't support a ternary operator and that two solutions are suggested to overcome this problem:

• define an anonymous function that wraps the if statement
• reformulate the expression to use a non-differentiable function like floor(), ceil(), sign(), dirac()

[gkronber]

Could this work?

log(x) (sign(x) + 1) / 2

[swinkler]

I suggest that we define a modified version of the log function for MATLAB that behaves like the log function used in HL:

function y = log_(x)
  if (x<=0)
    y = NaN;
  else
    y = log(x);

[gkronber]

looks nice

[swinkler]

Added special version of log function that behaves like Math.Log in r5022.

[swinkler]

Updated projects in exporters branch reacting on recent changes in the trunk (.NET 4.0, changes in interface of dataset) in r5180.

[gkronber]

r5416: Merged changes to symbolic expression encoding related to refactoring text-based export formats for symbolic expression trees.

[gkronber]

r5431: merged MATLAB formatter from branch into trunk and implemented formatting rules for new symbols related to dynamic modeling.

[swinkler]

Fixed bugs in r5433.

[gkronber]

Reviewed r5433. Thanks for fixing the bugs. This feature is ready for release.