Presentation on theme: "Learning Process-Based Models of Dynamic Systems Nikola Simidjievski Jozef Stefan Institute, Slovenia HIPEAC 2014 LJUBLJANA."— Presentation transcript:
Learning Process-Based Models of Dynamic Systems Nikola Simidjievski Jozef Stefan Institute, Slovenia HIPEAC 2014 LJUBLJANA
Introduction Equation Discovery (ED) is a subfield of machine learning, dealing with the task of inducing scientific laws and models in form of equations from observations. In the context of modeling system dynamics, the observations are time-series and the models take form of ordinary differential equations (ODEs) Process-Based Modeling (PBM) is an ED approach, which integrates domain-specific modeling knowledge and data into explanatory models of the observed systems. Using modeling knowledge formulated in a library, and observed data from the system at hand, this approach induces process-based models - an accurate, understandable and modular representation of the observed system dynamics.
Process-based models Conceptual (high-level) representation of system dynamics. Process-based models are comprised of entities and processes. Entities and processes represent specific components and interactions observed in the system. Entities represent the state/variable of the system. Processes the represent the interactions between the entities. Knowledge is represented as library of entity and process templates.
The task of learning process- based models Determining the structure of the model (ODE) Heuristic/exhaustive search over the space of suitable candidate models Parameter estimation finding values which minimize the difference (error) between simulated and measured (real) data 3 Inputs : Library (Domain specific) Conceptual model (Problem specific) Data (Task specific)
Process-Based Library Nataša Atanasova et al., Constructing a library of domain knowledge for automated modelling of aquatic ecosystems, Ecological Modelling, 2006 Library of domain-specific modeling knowledge
ProBMoT (Čerepnalkoski, Simidjievski, Tanevski et al.) ProBMoT 1 (Process Based Modeling Tool) Tool for complete modeling, parameter estimation and simulation of process-based models Darko Čerepnalkoski et al., The influence of parameter fitting methods on model structure selection in automated modeling of aquatic ecosystems, EM 2012
The Process Model generator Conceptual Model Library
The Process Specific models structures ~ 30 000 Model generator Library Conceptual Model
The Process Parameter Estimation Model generator Library Measurements Conceptual Model Specific models structures
The Process Parameter Estimation ~50K-100K Simulations per Structure Parameter Estimation Model generator Library Measurements Conceptual Model Specific models structures
Error values Best Model The Process Parameter Estimation Model generator Library Measurements Conceptual Model Validation
The Process Job Best Model Parameter Estimation Measurements Model generator Conceptual Model Library Validation
Improved predictive performance Better address the complexity of real systems: combination of base models for better description of observed behavior Training set T T1T1 T2T2 TNTN Model M 1 Model M 2 Model M N Learning algorithm Learning algorithm Learning algorithm Ensemble Ensembles
Ensembles of Process-based models Base models are homogeneous Training data is represented as a time series. Each base model is trained on different samples of the data (Bagging) 2-D space of candidate models A list of base models is generated by every ensemble iteration / replica
Sample of Measurements Parameter Estimation Model generator Conceptual Model Library
Parameter Estimation.................................... 100 Sample of Measurements Parameter Estimation Model generator Conceptual Model Library Sample of Measurements
Best Model 1 Best Model 2 Best Model 100 Parameter Estimation.................................... Let say 100 Sample of Measurements Parameter Estimation Model generator Conceptual Model Library Sample of Measurements Validation
Ensembles of Dynamic Systems Best Model 1 Best Model 2 Best Model 100............ ENSEMBLE MODEL
Parameter Estimation.................................... 100 Sample of Measurements Parameter Estimation Model generator Conceptual Model Library Sample of Measurements Job
Case Study : Population Dynamics in Lake Ecosystem Modeling phytoplankton dynamics in lake ecosystems (1 ODE) Lake Bled (Slovenia) Lake Kasumigaura (Japan) Lake Zurich (Switzerland) Lake Walensee (Switzerland)
Experiments Experimental Size 100 Ensemble Iterations 4 Different Lake Domains (Lake Bled, Lake Kasumigaura, Lake Zurich, Lake Walensee) Total of 40 different modeling scenarios ~200 Model Structures per scenario 50000 Iterations in the Parameter Estimation Phase per structure 1 Model (Structure Identification + Parameter Estimation) = 2- 3 minutes => Total Time of the whole experiment ~ 1,000,000min or ~ 2 years We did it in ….. 3 Days Nikola Simidjievski et al., Learning ensembles of population dynamics models and their application to modelling aquatic ecosystems., EM 2014
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