# Modelling & Simulations

**URL:** https://discourse.julialang.org/c/domain/models/21.md?page=61

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**Page:** 62

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## [Modelling COVID-19 in Julia and plotting AgentBasedModels on arbitrary networks](https://discourse.julialang.org/t/modelling-covid-19-in-julia-and-plotting-agentbasedmodels-on-arbitrary-networks/36005)

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**Author:** [@Datseris](https://discourse.julialang.org/u/Datseris)\
**Replies:** 8\
**Last updated:** [March 23, 2020, 2:48pm UTC](https://discourse.julialang.org/t/modelling-covid-19-in-julia-and-plotting-agentbasedmodels-on-arbitrary-networks/36005 "2020-03-23T14:48:05Z")

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Hi all! Recently there was a paper introducing Pathogen.jl, which I found interesting. It is a Julia package for modelling disease spreading : \[2002.05850\] Pathogen.jl: Infectious Disease Transmission Network Modelling …

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## [Define Truss Mesh in JuAFEM](https://discourse.julialang.org/t/define-truss-mesh-in-juafem/36191)

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**Author:** [@FrootLoops](https://discourse.julialang.org/u/FrootLoops)\
**Replies:** 3\
**Last updated:** [March 19, 2020, 4:01pm UTC](https://discourse.julialang.org/t/define-truss-mesh-in-juafem/36191 "2020-03-19T16:01:58Z")

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Hello everybody :slight\_smile: I am new to Julia and JuAFEM. Now I am trying to understand the linear Elasticity demo in juAFEM see. I understood a lot but I have big problems to adjust the code for my own purpose. I w…

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## [Global sensitivity analysis - following time series](https://discourse.julialang.org/t/global-sensitivity-analysis-following-time-series/35770)

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**Author:** [@alewolf](https://discourse.julialang.org/u/alewolf)\
**Replies:** 15\
**Last updated:** [March 18, 2020, 5:56pm UTC](https://discourse.julialang.org/t/global-sensitivity-analysis-following-time-series/35770 "2020-03-18T17:56:16Z")

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I tested the example in https://docs.juliadiffeq.org/stable/analysis/global\_sensitivity/#GSA-examples-1. As expected it all went well. This example, calculates sensitivity with regard to the mean over time on u1 and th…

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## [Why does LightGraphs.katz\_centrality give negative centrality scores?](https://discourse.julialang.org/t/why-does-lightgraphs-katz-centrality-give-negative-centrality-scores/21204)

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**Author:** [@ennvvy](https://discourse.julialang.org/u/ennvvy)\
**Replies:** 1\
**Last updated:** [March 18, 2020, 3:40am UTC](https://discourse.julialang.org/t/why-does-lightgraphs-katz-centrality-give-negative-centrality-scores/21204 "2020-03-18T03:40:29Z")

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I am using Katz\_centrality to determine the centrality measures for nodes in the network Julia 1.1.0. However, it yields negative values. Shouldn’t centrality scores be positive ?

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## [Trying to use Measurement.jl with DifferentialEquations.jl](https://discourse.julialang.org/t/trying-to-use-measurement-jl-with-differentialequations-jl/35655)

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**Author:** [@Hossein\_Haghi](https://discourse.julialang.org/u/Hossein_Haghi)\
**Replies:** 11\
**Last updated:** [March 6, 2020, 10:14pm UTC](https://discourse.julialang.org/t/trying-to-use-measurement-jl-with-differentialequations-jl/35655 "2020-03-06T22:14:23Z")

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In the example below I am trying to use Measurement.jl with DiffernetialEquations.jl to solve an ODE with error propagation. clearconsole() @time using DifferentialEquations, Measurements, MATLAB function Buckle(du,u,…

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## [Differential Equations General Questions](https://discourse.julialang.org/t/differential-equations-general-questions/34949)

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**Author:** [@alewolf](https://discourse.julialang.org/u/alewolf)\
**Replies:** 11\
**Last updated:** [February 24, 2020, 7:14pm UTC](https://discourse.julialang.org/t/differential-equations-general-questions/34949 "2020-02-24T19:14:53Z")

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Hi there - I had some complete package to work with differential equations montecarlo simulations. It seems that differentialequations montecarlo is not longer supported? Is differentialequations enesmble a replacemen…

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## [Issue with the incompressible elasticity example of JuAFEM package](https://discourse.julialang.org/t/issue-with-the-incompressible-elasticity-example-of-juafem-package/34814)

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**Author:** [@Leooop](https://discourse.julialang.org/u/Leooop)\
**Replies:** 3\
**Last updated:** [February 20, 2020, 12:33pm UTC](https://discourse.julialang.org/t/issue-with-the-incompressible-elasticity-example-of-juafem-package/34814 "2020-02-20T12:33:08Z")

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Hi, I plan to use the JuAFEM package as a basis for my phd work dealing with brittle damage modeling. First of all, I would like to thank the authors(@kristoffer.carlsson et @fredrikekre) for this beautifully written p…

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## [Performance problems with parallel ensemble simulation on GPU](https://discourse.julialang.org/t/performance-problems-with-parallel-ensemble-simulation-on-gpu/34596)

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**Author:** [@nnagyd](https://discourse.julialang.org/u/nnagyd)\
**Replies:** 3\
**Last updated:** [February 14, 2020, 8:06am UTC](https://discourse.julialang.org/t/performance-problems-with-parallel-ensemble-simulation-on-gpu/34596 "2020-02-14T08:06:32Z")

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We are doing some performance analysis of different ODE solvers on GPU’s. When I compare the run times of the Julia code to the odeint and MPGOS codes of the same system, Julia does not perform too well. We are solving t…

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## [How to make a callback including variables in definition](https://discourse.julialang.org/t/how-to-make-a-callback-including-variables-in-definition/34431)

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**Author:** [@xixit](https://discourse.julialang.org/u/xixit)\
**Replies:** 0\
**Last updated:** [February 10, 2020, 7:12pm UTC](https://discourse.julialang.org/t/how-to-make-a-callback-including-variables-in-definition/34431 "2020-02-10T19:12:33Z")

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Hi, I want to make a callback function set for my differential equation. The problem is I want to make it flexible so in future I can change any desireable callback function without changing the code. It’s a simple contr…

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## [Different results for same model with DifferentialEquations.jl](https://discourse.julialang.org/t/different-results-for-same-model-with-differentialequations-jl/34155)

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**Author:** [@moesphere](https://discourse.julialang.org/u/moesphere)\
**Replies:** 4\
**Last updated:** [February 4, 2020, 2:54pm UTC](https://discourse.julialang.org/t/different-results-for-same-model-with-differentialequations-jl/34155 "2020-02-04T14:54:52Z")

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I am defining two ODEProblems, where they are both the same but the implementation is different. There is a parameter I specify for one problem directly inside the function and for the other problem as an argument to the…

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## [How to save additional data in or with a solution when using DifferentialEquations](https://discourse.julialang.org/t/how-to-save-additional-data-in-or-with-a-solution-when-using-differentialequations/33892)

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**Author:** [@klaff](https://discourse.julialang.org/u/klaff)\
**Replies:** 2\
**Last updated:** [January 29, 2020, 2:41am UTC](https://discourse.julialang.org/t/how-to-save-additional-data-in-or-with-a-solution-when-using-differentialequations/33892 "2020-01-29T02:41:58Z")

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Is there an idiom for saving non-state variables in or with the solution? I would like to be able to list additional variables (either intermediate ones that I calculate anyway or derived ones of interest) and have them…

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## [Question on behavior with comparisons in MonteCarloMeasurements](https://discourse.julialang.org/t/question-on-behavior-with-comparisons-in-montecarlomeasurements/33679)

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**Author:** [@klaff](https://discourse.julialang.org/u/klaff)\
**Replies:** 7\
**Last updated:** [January 24, 2020, 8:54am UTC](https://discourse.julialang.org/t/question-on-behavior-with-comparisons-in-montecarlomeasurements/33679 "2020-01-24T08:54:35Z")

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I’m playing with MonteCarloMeasurements but running up against limitations around comparisons. julia\> a = Particles(1000, Uniform(0.0,10.0)) Part1000(5.0 ± 2.89) julia\> b = Particles(1000, Uniform(0.0, 10.0)) Part1000(…

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## [ForwardDiff: How to get the derivative part of a dual number](https://discourse.julialang.org/t/forwarddiff-how-to-get-the-derivative-part-of-a-dual-number/33560)

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**Author:** [@zdenek\_hurak](https://discourse.julialang.org/u/zdenek_hurak)\
**Replies:** 4\
**Last updated:** [January 20, 2020, 10:00am UTC](https://discourse.julialang.org/t/forwarddiff-how-to-get-the-derivative-part-of-a-dual-number/33560 "2020-01-20T10:00:20Z")

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How do I get the derivative part b (or whatever it is called) of a dual number given by a+b\\epsilon, \\quad \\epsilon^2=0, defined using ForwardDiff package? In particular, with the dual number 3+1\\epsilon given by julia\>…

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## [Finite element mesh interface](https://discourse.julialang.org/t/finite-element-mesh-interface/33325)

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**Author:** [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Replies:** 19\
**Last updated:** [January 16, 2020, 8:51am UTC](https://discourse.julialang.org/t/finite-element-mesh-interface/33325 "2020-01-16T08:51:24Z")

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Dear all, Do you know a paper, book or any published material that attempts to define an interface for general finite element meshes? I am in the process of finalizing a proposal interface, and would like to share it w…

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## [ModelingToolkit: variables in an expression and expression simplification](https://discourse.julialang.org/t/modelingtoolkit-variables-in-an-expression-and-expression-simplification/31894)

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**Author:** [@cvanaret](https://discourse.julialang.org/u/cvanaret)\
**Replies:** 6\
**Last updated:** [December 17, 2019, 12:26pm UTC](https://discourse.julialang.org/t/modelingtoolkit-variables-in-an-expression-and-expression-simplification/31894 "2019-12-17T12:26:43Z")

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Hi, I have two questions about the ModelingToolkit package: is there a function that determines the list of variables that occur in an expression? Example: x^2 + y - exp(y) contains x and y is there a function th…

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## [DifferentialEquations and Julia v 1.3?](https://discourse.julialang.org/t/differentialequations-and-julia-v-1-3/31688)

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**Author:** [@BLI](https://discourse.julialang.org/u/BLI)\
**Replies:** 6\
**Last updated:** [November 30, 2019, 2:29pm UTC](https://discourse.julialang.org/t/differentialequations-and-julia-v-1-3/31688 "2019-11-30T14:29:25Z")

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I just removed Julia v. 1.2 from my Windows 10 64bit laptop, installed Julia v.1.3, and renamed v1.2 in .julia\\environments to v1.3, and did \]instantiate. Then I updated packages, and do using DifferentialEquations. I ge…

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## [Encoding group elements and operations](https://discourse.julialang.org/t/encoding-group-elements-and-operations/30193)

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**Author:** [@jlapeyre](https://discourse.julialang.org/u/jlapeyre)\
**Replies:** 26\
**Last updated:** [November 14, 2019, 12:28am UTC](https://discourse.julialang.org/t/encoding-group-elements-and-operations/30193 "2019-11-14T00:28:30Z")

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Any ideas on efficient/convenient ways to encode group elements and operations ? In particular, I am interested in reducing strings of elements in a finite group by the group operation. But, I want to use them in other w…

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## [JuliaDiff and MPI](https://discourse.julialang.org/t/juliadiff-and-mpi/30983)

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**Author:** [@Kotaro\_Anno](https://discourse.julialang.org/u/Kotaro_Anno)\
**Replies:** 3\
**Last updated:** [November 12, 2019, 4:24pm UTC](https://discourse.julialang.org/t/juliadiff-and-mpi/30983 "2019-11-12T16:24:25Z")

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I’m interested in implementing both of JuliaDiff (automatic differentiation) and MPI. MPI needs domain decomposition, but I’m not sure JuliaDiff can deal with domain decomposition. And I can’t find good documents about…

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## [NLsolve always gives the initial guess as the final answer](https://discourse.julialang.org/t/nlsolve-always-gives-the-initial-guess-as-the-final-answer/30807)

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**Author:** [@huchiayu0517](https://discourse.julialang.org/u/huchiayu0517)\
**Replies:** 4\
**Last updated:** [November 11, 2019, 8:54am UTC](https://discourse.julialang.org/t/nlsolve-always-gives-the-initial-guess-as-the-final-answer/30807 "2019-11-11T08:54:39Z")

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Hi there! I’m trying to solve a nonlinear system of equations using the NLsolve package. However, I kept getting the same answer as my initial guess as if the solver did not do any iteration at all. I did not use Jacobia…

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## [VScode can't find reference in dev folder](https://discourse.julialang.org/t/vscode-cant-find-reference-in-dev-folder/29836)

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**Author:** [@affans](https://discourse.julialang.org/u/affans)\
**Replies:** 5\
**Last updated:** [October 16, 2019, 6:52pm UTC](https://discourse.julialang.org/t/vscode-cant-find-reference-in-dev-folder/29836 "2019-10-16T18:52:46Z")

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I have a package in my dev folder that I am developing locally. Typing in using pkgname in Julia REPL works well. However, in VSCode it can’t seem to find the reference (in my context I am writing unit tests for my packa…

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## [Building and solving a cascade of ODEs using DifferentialEquations](https://discourse.julialang.org/t/building-and-solving-a-cascade-of-odes-using-differentialequations/29963)

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**Author:** [@zdenek\_hurak](https://discourse.julialang.org/u/zdenek_hurak)\
**Replies:** 5\
**Last updated:** [October 16, 2019, 6:49pm UTC](https://discourse.julialang.org/t/building-and-solving-a-cascade-of-odes-using-differentialequations/29963 "2019-10-16T18:49:49Z")

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I want to build and solve a cascade of ODEs, by which term I mean that the first derivative of the k-th component of the vector x of (state) variables with respect to time t depends on x\_{k}(t) itself and on the precedin…

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## [Yet another question about solving an ODE with inputs using DifferentialEquations](https://discourse.julialang.org/t/yet-another-question-about-solving-an-ode-with-inputs-using-differentialequations/29960)

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**Author:** [@zdenek\_hurak](https://discourse.julialang.org/u/zdenek_hurak)\
**Replies:** 1\
**Last updated:** [October 15, 2019, 11:43pm UTC](https://discourse.julialang.org/t/yet-another-question-about-solving-an-ode-with-inputs-using-differentialequations/29960 "2019-10-15T23:43:01Z")

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This is yet another question related to the obviously popular basic problem of solving an ODE (or a system of ODEs) with inputs in Julia (using DifferentialEquations package). Let’s consider a single (scalar) ODE of the…

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## [ROS2 client library for Julia](https://discourse.julialang.org/t/ros2-client-library-for-julia/29929)

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**Author:** [@andreasziegler](https://discourse.julialang.org/u/andreasziegler)\
**Replies:** 0\
**Last updated:** [October 15, 2019, 8:47am UTC](https://discourse.julialang.org/t/ros2-client-library-for-julia/29929 "2019-10-15T08:47:16Z")

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As a robotics engineer, I’m working with ROS2. From an (software) engineering perspective, I’m quite interested in Julia however with the lack of a ROS2 client library for Julia, it’s for me currently a bit difficult to …

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## [Extracting local sensitivities when using save\_idxs](https://discourse.julialang.org/t/extracting-local-sensitivities-when-using-save-idxs/28714)

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**Author:** [@moesphere](https://discourse.julialang.org/u/moesphere)\
**Replies:** 5\
**Last updated:** [September 16, 2019, 8:05am UTC](https://discourse.julialang.org/t/extracting-local-sensitivities-when-using-save-idxs/28714 "2019-09-16T08:05:40Z")

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When specifying the saveat keyword, the extraction of local sensitivites seems to fail. The example is from the official documentation: using DifferentialEquations using DiffEqSensitivity function f(du,u,p,t) du\[1\] =…

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## [ApproxFun: defining a nonlinear differential operator](https://discourse.julialang.org/t/approxfun-defining-a-nonlinear-differential-operator/15296)

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**Author:** [@zdenek\_hurak](https://discourse.julialang.org/u/zdenek_hurak)\
**Replies:** 6\
**Last updated:** [September 12, 2019, 12:44pm UTC](https://discourse.julialang.org/t/approxfun-defining-a-nonlinear-differential-operator/15296 "2019-09-12T12:44:11Z")

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Hello, I am struggling with the very basics of usage of ApproxFun package. I would like to define a nonlinear differential operator (the ultimate motivation is actually to define and solve a nonlinear ODE). The operator \\…

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## [Creating functions with ModelingToolkit for parallel usage](https://discourse.julialang.org/t/creating-functions-with-modelingtoolkit-for-parallel-usage/27632)

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**Author:** [@jamblejoe](https://discourse.julialang.org/u/jamblejoe)\
**Replies:** 4\
**Last updated:** [September 5, 2019, 4:22am UTC](https://discourse.julialang.org/t/creating-functions-with-modelingtoolkit-for-parallel-usage/27632 "2019-09-05T04:22:08Z")

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Hi, after figuring out how to use ModelingToolkit to create functions/derivates etc. I would like to run code generated by ModelingToolkit in parallel. E.g. solving the Lorenz system for multiple initial states, see the…

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## [Information on auto-switching solvers](https://discourse.julialang.org/t/information-on-auto-switching-solvers/27853)

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**Author:** [@jamblejoe](https://discourse.julialang.org/u/jamblejoe)\
**Replies:** 2\
**Last updated:** [September 4, 2019, 9:11pm UTC](https://discourse.julialang.org/t/information-on-auto-switching-solvers/27853 "2019-09-04T21:11:26Z")

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Hi, I just want to know more about how the auto-switching algorithms in DifferentialEquations work. For example, when do they switch from non-stiff to stiff solver ? when do they switch back ? what happens to switchin…

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## [\[ANN\] QuasiMonteCarlo.jl](https://discourse.julialang.org/t/ann-quasimontecarlo-jl/28343)

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**Author:** [@cscherrer](https://discourse.julialang.org/u/cscherrer)\
**Replies:** 0\
**Last updated:** [September 3, 2019, 6:48pm UTC](https://discourse.julialang.org/t/ann-quasimontecarlo-jl/28343 "2019-09-03T18:48:24Z")

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I’ve started a library to make it convenient to do quasi Monte Carlo simulations. This leverages @stevengj’s Sobol.jl, @tkf’s Transducers.jl, and Mose Giordano et al’s Measurements.jl EDIT: Forgot to link to it: QuasiMo…

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## [Parallel computing using Parallel Ensemble Simulations (DiffEq) does not seem to work](https://discourse.julialang.org/t/parallel-computing-using-parallel-ensemble-simulations-diffeq-does-not-seem-to-work/28115)

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**Author:** [@Torkel](https://discourse.julialang.org/u/Torkel)\
**Replies:** 13\
**Last updated:** [August 30, 2019, 2:18pm UTC](https://discourse.julialang.org/t/parallel-computing-using-parallel-ensemble-simulations-diffeq-does-not-seem-to-work/28115 "2019-08-30T14:18:23Z")

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So i regularly run SDE simulations. To get a better idea of the systems behavior I would run several identical, and plot the various results. I figured this probably would be a good task for the Parallel Ensemble Simulat…

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## [Changing the righthand side in a callback](https://discourse.julialang.org/t/changing-the-righthand-side-in-a-callback/27462)

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**Author:** [@FHell](https://discourse.julialang.org/u/FHell)\
**Replies:** 6\
**Last updated:** [August 18, 2019, 6:31pm UTC](https://discourse.julialang.org/t/changing-the-righthand-side-in-a-callback/27462 "2019-08-18T18:31:31Z")

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Hi everyone, I am wondering how to correctly change the right hand side inside a DifferentialEquations callback. If I don’t reinit the system runs through but gives wrong results (compared to just running new different…

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