# Modelling & Simulations

**URL:** https://discourse.julialang.org/c/domain/models/21.md?page=15

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**Page:** 16

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## [Confusion in terminology dt & timing in agents.jl continuous time/EBM model](https://discourse.julialang.org/t/confusion-in-terminology-dt-timing-in-agents-jl-continuous-time-ebm-model/121748)

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**Author:** [@Sahil\_Khan](https://discourse.julialang.org/u/Sahil_Khan)\
**Replies:** 3\
**Last updated:** [October 30, 2024, 7:11am UTC](https://discourse.julialang.org/t/confusion-in-terminology-dt-timing-in-agents-jl-continuous-time-ebm-model/121748 "2024-10-30T07:11:34Z")

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Hello everyone, Im working with EBM continuous time model. Im little confused between dt given in model initiation function and timing term while defining events for model. It will be really helpful if someone can desc…

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## [How to perform practical identifiability in Julia?](https://discourse.julialang.org/t/how-to-perform-practical-identifiability-in-julia/121671)

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**Author:** [@Nick1](https://discourse.julialang.org/u/Nick1)\
**Replies:** 3\
**Last updated:** [October 30, 2024, 6:59am UTC](https://discourse.julialang.org/t/how-to-perform-practical-identifiability-in-julia/121671 "2024-10-30T06:59:20Z")

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Is there a way to perform practical identifiability in Julia? I have a systems biology problem with limited data and want to determine which parameters are practically identifiable.

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## [Scheduler errors when trying to graph agents](https://discourse.julialang.org/t/scheduler-errors-when-trying-to-graph-agents/121706)

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**Author:** [@tfranks](https://discourse.julialang.org/u/tfranks)\
**Replies:** 4\
**Last updated:** [October 29, 2024, 10:35pm UTC](https://discourse.julialang.org/t/scheduler-errors-when-trying-to-graph-agents/121706 "2024-10-29T22:35:05Z")

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Hello, I’ve created an agent-based model where depositor agents withdraw money from bank agents. I’m now trying to create a visual of the network by using Graphs.jl to show the banks as nodes and the depositors’ paths a…

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## [Non-linear analysis](https://discourse.julialang.org/t/non-linear-analysis/121890)

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**Author:** [@SergeantMike67](https://discourse.julialang.org/u/SergeantMike67)\
**Replies:** 18\
**Last updated:** [October 29, 2024, 9:34pm UTC](https://discourse.julialang.org/t/non-linear-analysis/121890 "2024-10-29T21:34:30Z")

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Having a bit of an issue and I don’t quite know where to turn. I have insect emergence data that fits a Gompertz model quite well. Example Data Row │ ED Wasp │ Float64 Float64 ─────┼────────────────── 1 │ 14…

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## [BifurcationKit.jl: Continuation of non-autonomous ODE limit cycle](https://discourse.julialang.org/t/bifurcationkit-jl-continuation-of-non-autonomous-ode-limit-cycle/121871)

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**Author:** [@mjowen](https://discourse.julialang.org/u/mjowen)\
**Replies:** 0\
**Last updated:** [October 28, 2024, 2:40pm UTC](https://discourse.julialang.org/t/bifurcationkit-jl-continuation-of-non-autonomous-ode-limit-cycle/121871 "2024-10-28T14:40:33Z")

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Hi, I have a non-autonomous periodic ODE system and I want to use BifurcationKit to run continuation on the limit cycle. The system features a periodic discontinuous forcing function I\_St. I have followed the steps here …

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## [Enforce positivity in simple PDE solution](https://discourse.julialang.org/t/enforce-positivity-in-simple-pde-solution/121738)

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**Author:** [@ify](https://discourse.julialang.org/u/ify)\
**Replies:** 5\
**Last updated:** [October 28, 2024, 10:35am UTC](https://discourse.julialang.org/t/enforce-positivity-in-simple-pde-solution/121738 "2024-10-28T10:35:57Z")

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Hi all, Pretty new to julia. I am trying to solve a simplified PDE that I normally would do in R. In R, the numerical steady state solution can be constrained to obtain solution concentration. However, when I translate …

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## [Using StaticArrays with EnsembleAnalysis runs with SDEProblem but not ODEProblem](https://discourse.julialang.org/t/using-staticarrays-with-ensembleanalysis-runs-with-sdeproblem-but-not-odeproblem/121837)

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**Author:** [@gjgress](https://discourse.julialang.org/u/gjgress)\
**Replies:** 2\
**Last updated:** [October 28, 2024, 10:11am UTC](https://discourse.julialang.org/t/using-staticarrays-with-ensembleanalysis-runs-with-sdeproblem-but-not-odeproblem/121837 "2024-10-28T10:11:26Z")

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Context: In my personal project I am working with running ensemble problems of SDEs. To improve performance, I used SVectors wherever possible. Depending on my needs, I used componentwise\_vectors\_timepoint to interpolat…

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## [Linear parameter varying control (LPV control)](https://discourse.julialang.org/t/linear-parameter-varying-control-lpv-control/121840)

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**Author:** [@ufechner7](https://discourse.julialang.org/u/ufechner7)\
**Replies:** 8\
**Last updated:** [October 28, 2024, 9:14am UTC](https://discourse.julialang.org/t/linear-parameter-varying-control-lpv-control/121840 "2024-10-28T09:14:30Z")

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I am trying to implement an LPV controller based on GitHub - JuliaControl/DiscretePIDs.jl: Discrete-time PID controllers in Julia The idea is easy: Use a controller for heading/ course with an inner and an outer loop. T…

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## [StochasticDelayDiffEq having trouble with stiff models \[solved\]](https://discourse.julialang.org/t/stochasticdelaydiffeq-having-trouble-with-stiff-models-solved/121725)

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**Author:** [@kmd](https://discourse.julialang.org/u/kmd)\
**Replies:** 2\
**Last updated:** [October 26, 2024, 7:58pm UTC](https://discourse.julialang.org/t/stochasticdelaydiffeq-having-trouble-with-stiff-models-solved/121725 "2024-10-26T19:58:14Z")

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I am using SciML to try to integrate a stiff model with small noise. It is giving me tons of grief though, and I am not sure how to approach it. I even tried setting tolerances to very small values & increasing maxiter…

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## [Component-based model for N reactors connected to a tank](https://discourse.julialang.org/t/component-based-model-for-n-reactors-connected-to-a-tank/119536)

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**Author:** [@cstjean](https://discourse.julialang.org/u/cstjean)\
**Replies:** 9\
**Last updated:** [October 24, 2024, 8:29am UTC](https://discourse.julialang.org/t/component-based-model-for-n-reactors-connected-to-a-tank/119536 "2024-10-24T08:29:25Z")

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Say I’ve got 10 chemical reactors, which all flow into a single tank. The reactors all have different production rates for some species S. I’m interested in the concentration of S in the reactors and in the tank. I guess…

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## [How to override defaults with u0 in solve](https://discourse.julialang.org/t/how-to-override-defaults-with-u0-in-solve/121629)

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**Author:** [@Bart\_van\_de\_Lint](https://discourse.julialang.org/u/Bart_van_de_Lint)\
**Replies:** 2\
**Last updated:** [October 24, 2024, 5:02am UTC](https://discourse.julialang.org/t/how-to-override-defaults-with-u0-in-solve/121629 "2024-10-24T05:02:41Z")

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I have an ODEProblem with a system with default values, and with a starting state prob.u0. I want to be able to solve this problem from an arbitrary starting state u0 to the next timestep using solve(prob, QNDF(); save\_s…

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## [Changing the size of VectorContinuousCallback](https://discourse.julialang.org/t/changing-the-size-of-vectorcontinuouscallback/119534)

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**Author:** [@evan-wehi](https://discourse.julialang.org/u/evan-wehi)\
**Replies:** 6\
**Last updated:** [October 23, 2024, 5:40am UTC](https://discourse.julialang.org/t/changing-the-size-of-vectorcontinuouscallback/119534 "2024-10-23T05:40:56Z")

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I’m modelling cell population dynamics. Cells die and divide so the size of system is always changing. I love DifferentialEquations.jl because it is the only library I know of that has an API for this. Most of my state v…

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## [Events seemingly ignored in system model](https://discourse.julialang.org/t/events-seemingly-ignored-in-system-model/121605)

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**Author:** [@jmaedler](https://discourse.julialang.org/u/jmaedler)\
**Replies:** 1\
**Last updated:** [October 22, 2024, 10:47pm UTC](https://discourse.julialang.org/t/events-seemingly-ignored-in-system-model/121605 "2024-10-22T22:47:34Z")

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Hi guys, I am running into an issue simulating a system model. Fundamentally it is two valves in sequence between two pressure sources. This is a test for the valve models which should allow these scenarios for a virtua…

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## [Sparse variable arrays and creation of ODESystem's](https://discourse.julialang.org/t/sparse-variable-arrays-and-creation-of-odesystems/121335)

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**Author:** [@johannesnauta](https://discourse.julialang.org/u/johannesnauta)\
**Replies:** 1\
**Last updated:** [October 21, 2024, 8:41am UTC](https://discourse.julialang.org/t/sparse-variable-arrays-and-creation-of-odesystems/121335 "2024-10-21T08:41:40Z")

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Sketch of the problem: a dumb example I have a question about the ability of ‘enforcing’ sparsity of a specific variable array that is created with the @variables macro. When running experiments, I have noticed that cre…

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## [Switching behaviour of implicit ODEs](https://discourse.julialang.org/t/switching-behaviour-of-implicit-odes/121472)

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**Author:** [@clm](https://discourse.julialang.org/u/clm)\
**Replies:** 7\
**Last updated:** [October 20, 2024, 12:19am UTC](https://discourse.julialang.org/t/switching-behaviour-of-implicit-odes/121472 "2024-10-20T00:19:51Z")

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I have two coupled nonlinear ODEs where I’m aiming to find x(t) and y(t), defined generally as: f(x,y,x',y') = 0, \\min(g(x,y,x',y'),h(x,y,x',y')) = 0, where I expect that I will switch between g\<h and g\>h at least onc…

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## [Error with @discrete\_events for composite model (reeval\_internals\_due\_to\_modification!)](https://discourse.julialang.org/t/error-with-discrete-events-for-composite-model-reeval-internals-due-to-modification/121486)

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**Author:** [@jmaedler](https://discourse.julialang.org/u/jmaedler)\
**Replies:** 2\
**Last updated:** [October 19, 2024, 10:42pm UTC](https://discourse.julialang.org/t/error-with-discrete-events-for-composite-model-reeval-internals-due-to-modification/121486 "2024-10-19T22:42:47Z")

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Hi everyone, I am building a composite model in order to test my binary valve model and I am running into an error, which I do not understand. This is the code for building up the system and running it. I can also provi…

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## [Different solution if solving a differential equation in chunks or for full time at once](https://discourse.julialang.org/t/different-solution-if-solving-a-differential-equation-in-chunks-or-for-full-time-at-once/121351)

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**Author:** [@shaurya](https://discourse.julialang.org/u/shaurya)\
**Replies:** 5\
**Last updated:** [October 16, 2024, 9:56pm UTC](https://discourse.julialang.org/t/different-solution-if-solving-a-differential-equation-in-chunks-or-for-full-time-at-once/121351 "2024-10-16T21:56:30Z")

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Hi! I’m trying a simulate an orbit in the chaotic 3 body dynamics, and perform two different simulations: one for full time (0, nT) where n is an integer and T is the time period of the orbit. On the other hand, I also p…

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## [How to dynamically assign unique names to models in a loop with @named in ModelingToolkit](https://discourse.julialang.org/t/how-to-dynamically-assign-unique-names-to-models-in-a-loop-with-named-in-modelingtoolkit/121367)

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**Author:** [@DanaO](https://discourse.julialang.org/u/DanaO)\
**Replies:** 1\
**Last updated:** [October 16, 2024, 10:20am UTC](https://discourse.julialang.org/t/how-to-dynamically-assign-unique-names-to-models-in-a-loop-with-named-in-modelingtoolkit/121367 "2024-10-16T10:20:14Z")

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Hi everyone, I’m working on a simulation of a gas network using ModelingToolkit in Julia, where I create multiple Pipe models inside a loop. My issue is that I need to assign unique names to each pipe created in the loo…

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## [Evolving a DynamicalSystem until it is close to an attractor](https://discourse.julialang.org/t/evolving-a-dynamicalsystem-until-it-is-close-to-an-attractor/121294)

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**Author:** [@andreasmorr](https://discourse.julialang.org/u/andreasmorr)\
**Replies:** 2\
**Last updated:** [October 15, 2024, 11:16am UTC](https://discourse.julialang.org/t/evolving-a-dynamicalsystem-until-it-is-close-to-an-attractor/121294 "2024-10-15T11:16:34Z")

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Hello! I’ve been working with DynamicalSystems.jl and Attractors.jl and I’m wondering if there exists the following functionality: I would like to obtain a trajectory of a given DynamicalSystem and initial condition, wh…

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## [Problem installing Gridap.jl Tutorials](https://discourse.julialang.org/t/problem-installing-gridap-jl-tutorials/121306)

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**Author:** [@uri](https://discourse.julialang.org/u/uri)\
**Replies:** 0\
**Last updated:** [October 14, 2024, 9:07pm UTC](https://discourse.julialang.org/t/problem-installing-gridap-jl-tutorials/121306 "2024-10-14T21:07:57Z")

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I followed all the steps to install the Gridap.jl Tutorials, but when I try to instantiate the project it didin’t precompile 11 dependencies: (Tutorials) pkg\> instantiate Precompiling project… ✗ Algoim ✗ Conda ✗ Min…

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## [Finding steady-states symbolicaly](https://discourse.julialang.org/t/finding-steady-states-symbolicaly/119545)

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**Author:** [@adhalanay](https://discourse.julialang.org/u/adhalanay)\
**Replies:** 17\
**Last updated:** [October 14, 2024, 3:06pm UTC](https://discourse.julialang.org/t/finding-steady-states-symbolicaly/119545 "2024-10-14T15:06:05Z")

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Maybe the question is trivial, but I cannot find an answer. Using Catalyst.jl I introduced a reaction network rn and constructed the corresponding system of ODEs with convert(ODESystem,rn). The system has a number of pa…

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## [Stream Connections of Subsystems](https://discourse.julialang.org/t/stream-connections-of-subsystems/121279)

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**Author:** [@Sebastian\_Schmitt](https://discourse.julialang.org/u/Sebastian_Schmitt)\
**Replies:** 2\
**Last updated:** [October 14, 2024, 1:20pm UTC](https://discourse.julialang.org/t/stream-connections-of-subsystems/121279 "2024-10-14T13:20:48Z")

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Hi, I have a system with two subsystems (which themself have two connectors with stream variables). I want to connect the connectors of the subsystem in the main system using ModelingToolkit using ModelingToolkit: t\_nou…

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## [MTK bugging for spacing between variable and operation?](https://discourse.julialang.org/t/mtk-bugging-for-spacing-between-variable-and-operation/121278)

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**Author:** [@Sushrut\_Deshpande](https://discourse.julialang.org/u/Sushrut_Deshpande)\
**Replies:** 2\
**Last updated:** [October 14, 2024, 10:02am UTC](https://discourse.julialang.org/t/mtk-bugging-for-spacing-between-variable-and-operation/121278 "2024-10-14T10:02:31Z")

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Hello, I have a toy replication of a problem I have faced. using ModelingToolkit, DifferentialEquations @independent\_variables t @connector function myConnector(;name) vars = @variables begin x(t), \[inpu…

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## [Performance of derivatives of Ensemble problem](https://discourse.julialang.org/t/performance-of-derivatives-of-ensemble-problem/121167)

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**Author:** [@stochasticguy](https://discourse.julialang.org/u/stochasticguy)\
**Replies:** 2\
**Last updated:** [October 12, 2024, 6:34pm UTC](https://discourse.julialang.org/t/performance-of-derivatives-of-ensemble-problem/121167 "2024-10-12T18:34:29Z")

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Hi everyone, I’m working on simulating trajectories of a Geometric Brownian Motion (GBM) and calculating sensitivities using automatic differentiation. I’m comparing two approaches: Custom GBM implementation where I d…

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## [Put linear ODE system in matrix-vector form](https://discourse.julialang.org/t/put-linear-ode-system-in-matrix-vector-form/121170)

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**Author:** [@langestefan](https://discourse.julialang.org/u/langestefan)\
**Replies:** 5\
**Last updated:** [October 12, 2024, 1:51pm UTC](https://discourse.julialang.org/t/put-linear-ode-system-in-matrix-vector-form/121170 "2024-10-12T13:51:51Z")

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Hi, I am trying to put my linear ODE system in state space form. My model is quite simple: function TiThTe(input\_funcs::Dict) @parameters begin C\_i C\_e C\_h R\_ie R\_ih …

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## [Unexpected(?) behavior using ModelingToolkit.jl, discrete\_events and irreducible](https://discourse.julialang.org/t/unexpected-behavior-using-modelingtoolkit-jl-discrete-events-and-irreducible/121142)

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**Author:** [@jmaedler](https://discourse.julialang.org/u/jmaedler)\
**Replies:** 2\
**Last updated:** [October 12, 2024, 1:40pm UTC](https://discourse.julialang.org/t/unexpected-behavior-using-modelingtoolkit-jl-discrete-events-and-irreducible/121142 "2024-10-12T13:40:24Z")

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Hi everyone, I am running into an issues using discrete events and irreducible variables in ModelingToolkit.jl. I hope the following example is sufficent as an MWE. It is a composite model of two tanks in sequence which…

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## [Local Error Estimation for DAEs](https://discourse.julialang.org/t/local-error-estimation-for-daes/121159)

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**Author:** [@aaliqureshi](https://discourse.julialang.org/u/aaliqureshi)\
**Replies:** 7\
**Last updated:** [October 11, 2024, 3:09pm UTC](https://discourse.julialang.org/t/local-error-estimation-for-daes/121159 "2024-10-11T15:09:15Z")

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I’m inquiring about the error estimation approach used for solving Differential Algebraic Equations (DAEs) in Julia. The current approach considers all variables (state and algebraic) in the estimation of local error. H…

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## [Slow indexing of constant-valued variables in MTK](https://discourse.julialang.org/t/slow-indexing-of-constant-valued-variables-in-mtk/120922)

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**Author:** [@bspanoghe](https://discourse.julialang.org/u/bspanoghe)\
**Replies:** 8\
**Last updated:** [October 11, 2024, 8:42am UTC](https://discourse.julialang.org/t/slow-indexing-of-constant-valued-variables-in-mtk/120922 "2024-10-11T08:42:17Z")

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Hi I’m currently working with large hierarchical models in ModelingToolkit.jl and found that indexing the solution with constant-valued variables becomes incredibly slow for larger systems. This results in plotting of t…

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## [Specific Dom](https://discourse.julialang.org/t/specific-dom/121140)

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**Author:** [@finmod](https://discourse.julialang.org/u/finmod)\
**Replies:** 1\
**Last updated:** [October 10, 2024, 12:08pm UTC](https://discourse.julialang.org/t/specific-dom/121140 "2024-10-10T12:08:55Z")

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Bringing sfctools for economic agents in python to Agents.jl Is Agents.jl able to create and simulate economic agents as in: Economic Agents — sfctools documentation

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## [MTK & units: how to specify unit for time?](https://discourse.julialang.org/t/mtk-units-how-to-specify-unit-for-time/121138)

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**Author:** [@BLI](https://discourse.julialang.org/u/BLI)\
**Replies:** 2\
**Last updated:** [October 10, 2024, 11:41am UTC](https://discourse.julialang.org/t/mtk-units-how-to-specify-unit-for-time/121138 "2024-10-10T11:41:30Z")

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I’ve started to experiments with units for models. My question is probably related to how I can specify units for time when I do: using ModelingToolkit: t\_nounits as t, D\_nounits as Dt How can I specify unit for t so …

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