Parameters ยป |
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In the Parameters Node, you may add bounds on the Mass Action kinetic parameters: PreExponential Factors, Activation Energy and Orders. Bounds for LHHW Site parameters can also be defined when one or more Sites defined in the Chemistry → Kinetics → Parameters are assigned to reactions in the Chemistry → Kinetics → Kinetics Sites node. You may also set bounds for the stoichiometric coefficients if this feature was enabled in the Estimation node. Bounds on the reaction rates can also be entered here. Actions Tabbed Views Mass Action LHHW Sites Stoichiometry Rate Bounds
Mass Action
Top of Topic For Mass Action Reactions, the information entered in this tab describes all their kinetics. For LHHW Reactions, the information entered here is for the numerator of the LHHW Kinetics.
Grid Views Reaction Parameters - Initial Estimates [Rate Units] Reaction Name Orders
Reaction Parameters - Initial Estimates [Rate Units]
Note:You may run Solver → CheckModel to verify that the bounds have been entered correctly.This grid displays the list of Reactions and the values of their kinetic parameters. The grid is organized in columns as explained below:
Reaction Name Orders This grid depends on the first Reaction Parameters grid, and displays the compounds affecting each reaction with their order. This grid is organized in columns as explained below:
LHHW Sites
Top of Topic The LHHW Sites tab is used to add bounds on the parameters of the LHHW Sites. This tab is shown when one or more Sites defined in the Chemistry → Kinetics → Parameters are assigned to one or more reactions in Chemistry → Kinetics → Kinetics Sites node.
Grid Views Sites Site Name: Terms Site Name - Term Name: Orders
Sites
Note:You may run Solver → CheckModel to verify that the bounds have been entered correctly.This grid displays the list of LHHW sites and their properties.The grid is read-only and it is organized in columns as explained below:
Site Name: Terms This grid displays the list of terms for the site selected in the first (LHHW Sites) grid. It is organized in columns as explained below:
Site Name - Term Name: Orders This grid depends on the selected site in the LHHW sites grid and the selected term in the Terms grid. For each site-term pair, this grid displays the compounds with their orders. The grid is organized in columns as explained below:
Stoichiometry
This tab is only shown when the Estimate Stoichiometric Coefficients action is enabled in Estimation node.
Grid Views Reactions Stoichiometry: Reaction Name
Reactions
This grid displays the list of included Reactions in the project. Stoichiometry: Reaction Name Here, you may enter bounds for the stoichiometric coefficients. By default all bounds are closed. It is organized in columns as described below:
Top of Topic
Rate Bounds
Top of Topic In this tab you can define bounds for the reaction rates, and they are applied for all included sets when the option Use Rate Bounds is enabled in Solution Options node. The default values are -1E+08 for the lower bounds and 1E+08 for the upper bounds, effectively resulting in an unconstrained system. Actions Initialize Mass Action Bounds Initialize LHHW Sites Bounds Initialize Stoichiometry Bounds Initialize Parameters Quick Run Open Solver
Initialize Mass Action Bounds
Top of Topic Initialize Bounds is used to fill automatically the kinetic parameters and/or order bounds. It has two sub-actions: Current Values With this option you can autofill the minimum and maximum values with the current values By Percent of Current This action is used to enter the bounds as percentage of the current values. On executing Initialize Bounds → By Percent of Current, a Parameters Dialog appears, requesting additional information:
Initialize LHHW Sites Bounds Initialize Bounds is used to fill automatically the parameter bounds for the LHHW Sites. It has the same sub-actions as in Initialize Mass Action Bounds. Initialize Stoichiometry Bounds Initialize Bounds is used to fill the bounds for the Stoichiometric Coefficients. It has the same sub-actions as Initialize Mass Action Bounds. Initialize Parameters This action should only be used in the early stage of model building when you are trying to get the first feasible simulation. In a new model, simulations sometimes fail due to poor initial guesses of the kinetic parameters or Initialization Values. This feature provides a smart guess of the kinetic parameters to improve solver reliability. When executing this action, the mass action preexponentials and activation energies are internally computed using a simplified mass action model and loaded as values here. Site parameters are not changed. You should take into account that original values entered are overwritten by this action. The internal calculation consists of a Runge Kutta integration followed by adjusting the parameters to minimize a cost function. This cost function represents a weighted least square objective and is calculated based on the Weights and data available in Experiments. A sequential adjustment of the kinetic parameters is done after each integration to minimize the cost function. A 15 second timeout is applied to prevent excessive iterations since the purpose is only to initialize the model. In addition to the kinetic parameters, the method also fills the Total Moles tab of the Initialization Values node. You can use them in the run by having Warmstart option set as Use Provided Initial Values. REX also has an alternative initialization method that is directly implemented in the solver. If the above method fails to give a feasible solution, you can use the the Autoinitialize Parameters option to initialize the kinetic parameters. Please note that when you execute the Initialize Parameters action, this Autoinitialize Parameters flag is turned OFF. See Also: |
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