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Hello team, I am working on a population pharmacokinetics (PK) project, so I am using sbiofitmixed() to solve the model. However, I found that the fit program code directly exported from Simbiology Model Analyzer gave me different results from my custom code. Although I have all the settings set as the same, I have a problem with the parameter estimation on ka_Central. My Simbiology Model Analyzer code can estimate this parameter with high confidence, but my custom code cannot. I tried debugging but could not find where the problem came from. Please find the code in the attachment file. Thank you very much. Jesse

Hello, I have a question regarding sbiofitmixed. I have fitted a model using log parameter transformation. In the NLMEresults object I can see the transformed values of the fixed effects in conjunction with their standard errors. While I can extract the original non-transformed values of the fixed effect by either using exp to transform them back or extracting them from the NLMEResults.PopulationParameterEstimates field, I can not do the same with the standard errors. I could in theory use the Delta method but I have a small sample size so that is not a proper idea here. My question is if there is a way to extract the back-tranformed Standard Errors of the model fit using sbiofitmixed or the NLMEResults object? Thank you for your answers in advance. Best, Ben

Hello, I have a question regarding the regression tools in SimBiology. I have an ODE model which I would like to fit for a given dataset using sbiofit or sbiofitmixed. When i want to find some parameter set using sbiofitmixed, the ODE model can return with invalid values (e.g. complex, NaN or Inf) which completely halts the search process. My experience with sbiofit is that the algorithms can recover from these values (as opposed to sbiofitmixed) for the vast majority of cases, but in some occasion the procedure still halts. Even if I set bounds on my parameters, there could be a (hidden) nonlinear relationship which makes the ODE invalid for a specific combination of the fitted parameter values. The following error message can occur using sbiofitmixed: Error using sbiofitmixed (line 249) A simulation errored or returned NaN, Inf, or complex values during parameter estimation. This typically indicates that the estimated parameter values converged to values that are invalid for the model. My question is if there is any way to recover sbiofitmixed from these parameter values? For example defining an event during the ODE simulation which stops the integration. It would be nice, if there was a way to find a different trial point for the current iteration in such cases for the algorithm. Bonus question: Is there any 'best practice' in the literature to handle these situations? For example if I code the algorithm by hand, I could just stop the integration if some state variable exceeds some given value. At these instances I could just set the cost function to some high value (for example 1e5), however I have a gut feeling that this is not the best solution for this issue. Thank you in advance, Ben

I’m interested in performing a non-linear mixed effect estimation of a compartmental model. Besides the four parameters to be estimated, the model has two parameters which need to be fixed and which assume a different value for each subject in the dataset. Is there any way to change the value of the fixed parameter for each subject in the dataset? Thank you!