Tools and Methods for Analysis, Debugging, and Performance Improvement of Equation-Based Models

Abstract

Equation-based object-oriented (EOO) modeling languages such as Modelica provide a convenient, declarative method for describing models of cyber-physical systems. Because of the ease of use of EOO languages, large and complex models can be built with limited effort. However, current state-of-the-art tools do not provide the user with enough information when errors appear or simulation results are wrong. It is of paramount importance that such tools should give the user enough information to correct errors or understand where the problems that lead to wrong simulation results are located. However, understanding the model translation process of an EOO compiler is a daunting task that not only requires knowledge of the numerical algorithms that the tool executes during simulation, but also the complex symbolic transformations being performed.As part of this work, methods have been developed and explored where the EOO tool, an enhanced Modelica compiler, records the transformations during the translation process in order to provide better diagnostics, explanations, and analysis. This information is used to generate better error-messages during translation. It is also used to provide better debugging for a simulation that produces unexpected results or where numerical methods fail.Meeting deadlines is particularly important for real-time applications. It is usually essential to identify possible bottlenecks and either simplify the model or give hints to the compiler that enable it to generate faster code. When profiling and measuring execution times of parts of the model the recorded information can also be used to find out why a particular system model executes slowly.Combined with debugging information, it is possible to find out why this system of equations is slow to solve, which helps understanding what can be done to simplify the model. A tool with a graphical user interface has been developed to make debugging and performance profiling easier. Both debugging and profiling have been combined into a single view so that performance metrics are mapped to equations, which are mapped to debugging information.The algorithmic part of Modelica was extended with meta-modeling constructs (MetaModelica) for language modeling. In this context a quite general approach to debugging and compilation from (extended) Modelica to C code was developed. That makes it possible to use the same executable format for simulation executables as for compiler bootstrapping when the compiler written in MetaModelica compiles itself.Finally, a method and tool prototype suitable for speeding up simulations has been developed. It works by partitioning the model at appropriate places and compiling a simulation executable for a suitable parallel platform. Populärvetenskaplig sammanfattningSom ingenjör lär man sig att förstå världen genom ekvationer. För att beskriva eller modellera ett fysikaliskt system, till exempel vid utveckling av en produkt, vill ingenjören använda sig av de ekvationer som han eller hon lärt sig från böcker eller fö...

Integrated Debugging of Equation-Based Models

“…This paper presents the integrated debugger of the OpenModelica tool suite, including a graphical user interface integrated with the OpenModelica Connection Editor (OMEdit) GUI. This builds on and extends previous results from a transformational static equation debugger [6] [7] and a dynamic debugger [1][3] [4] for the algorithmic subset of Modelica.…”

“…The underlying implementation of the transformation tracing mechanism is described in more detail in [7]. Some further improvements are present in this version.…”

“…Sjölund [7] is used as the main basis of the equation debugging part of this work. It was mainly focused on tracing operations in the compiler backend.…”

“…The key idea introduced in [7] is to encode and store in a list all transformations that are performed by the Modelica compiler on the model equations, such as symbolic solution, alias elimination, symbolic differen- The XML-file contains all the variables and equations used to solve the model, as well as variables that have already been solved for, alias relations, and so on. The equations are split into several groups, such as startvalue equations, initial equations, regular equations, since the same variable may have different equations defined for it in different phases of the program.…”

Industrial Evaluation of Integrated Performance Analysis and Equation Model Debugging for Equation-Based Models

“…As described in Sjölund (2015), the techniques used when proling Modelica equation-based models are quite dierent from proling of general programs (Graham et al, 1983). Some earlier more limited approaches to proling Modelica models are presented by Huhn et al (2011) and Schulze et al (2010).…”