# Modelling & Simulations

**URL:** https://discourse.julialang.org/c/domain/models/21.md?page=62

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**Page:** 63

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## [Grassman algebras for electromagnetic scattering](https://discourse.julialang.org/t/grassman-algebras-for-electromagnetic-scattering/27681)

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**Author:** [@chakravala](https://discourse.julialang.org/u/chakravala)\
**Replies:** 7\
**Last updated:** [August 18, 2019, 2:53pm UTC](https://discourse.julialang.org/t/grassman-algebras-for-electromagnetic-scattering/27681 "2019-08-18T14:53:05Z")

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All of the math you are trying to do here could be simplified by using Grassmann.jl multivectors instead of matrices. It encodes both rotational algebras as well as spacetime geometry, so that matrices are no longer need…

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## [DAEs and initialization](https://discourse.julialang.org/t/daes-and-initialization/27648)

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**Author:** [@BLI](https://discourse.julialang.org/u/BLI)\
**Replies:** 1\
**Last updated:** [August 17, 2019, 11:33am UTC](https://discourse.julialang.org/t/daes-and-initialization/27648 "2019-08-17T11:33:07Z")

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I need to use DAE formulation of models, and wonder about the initialization… From the documentation: Question: Does this imply that those differential\_vars which are differential, are assumed to have correct initial…

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## [Calculating Lyapunov Exponents with ModelingToolkit](https://discourse.julialang.org/t/calculating-lyapunov-exponents-with-modelingtoolkit/26641)

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**Author:** [@jamblejoe](https://discourse.julialang.org/u/jamblejoe)\
**Replies:** 17\
**Last updated:** [August 14, 2019, 10:49am UTC](https://discourse.julialang.org/t/calculating-lyapunov-exponents-with-modelingtoolkit/26641 "2019-08-14T10:49:52Z")

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Hi all, suggested in this thread here Chaostools tangent\_integrator stiff solvers - #26 by jamblejoe, one could use ModelingToolkit the approach the following scenario. One has a dynamical system defined by n different…

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## [Best practices for parallel generation of pseudo-random numbers](https://discourse.julialang.org/t/best-practices-for-parallel-generation-of-pseudo-random-numbers/26504)

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**Author:** [@non-Jedi](https://discourse.julialang.org/u/non-Jedi)\
**Replies:** 11\
**Last updated:** [July 25, 2019, 3:35pm UTC](https://discourse.julialang.org/t/best-practices-for-parallel-generation-of-pseudo-random-numbers/26504 "2019-07-25T15:35:08Z")

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I’m relatively new to the world of simulation and am running some discrete event simulations using SimJulia.jl and Distributions.jl for a graduate-level class. I noticed that the Wikipedia article for Mersenne Twister (w…

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## [Julia and Demography](https://discourse.julialang.org/t/julia-and-demography/23773)

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**Author:** [@sbacelar](https://discourse.julialang.org/u/sbacelar)\
**Replies:** 9\
**Last updated:** [July 22, 2019, 7:16am UTC](https://discourse.julialang.org/t/julia-and-demography/23773 "2019-07-22T07:16:54Z")

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Is there any work on (computational) demography using Julia?

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## [Chaostools tangent\_integrator stiff solvers](https://discourse.julialang.org/t/chaostools-tangent-integrator-stiff-solvers/26464)

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**Author:** [@jamblejoe](https://discourse.julialang.org/u/jamblejoe)\
**Replies:** 27\
**Last updated:** [July 18, 2019, 1:21pm UTC](https://discourse.julialang.org/t/chaostools-tangent-integrator-stiff-solvers/26464 "2019-07-18T13:21:34Z")

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Hi, I want to use the tangent\_integrator function from the ChaosTools package with solvers for stiff problems: integ = tangent\_integrator(cds, w0; alg=Rodas5(), abstol=1e-9, reltol=1e-9) step!(integ, 1.0) but this giv…

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## [Issue with ODE solver for solving Burgers equation using spectral method](https://discourse.julialang.org/t/issue-with-ode-solver-for-solving-burgers-equation-using-spectral-method/26224)

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**Author:** [@henry2004y](https://discourse.julialang.org/u/henry2004y)\
**Replies:** 1\
**Last updated:** [July 10, 2019, 3:26pm UTC](https://discourse.julialang.org/t/issue-with-ode-solver-for-solving-burgers-equation-using-spectral-method/26224 "2019-07-10T15:26:04Z")

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Hi all, I am trying to solve the 1D Burgers equation Burgers equation wiki using Fourier transform and the ODE package. Things works smoothly in Matlab, but not in Julia. I’m just wondering where I went wrong. Matlab …

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## [Declaring state-dependent delay with DDEProblem; simulation gets slower?](https://discourse.julialang.org/t/declaring-state-dependent-delay-with-ddeproblem-simulation-gets-slower/26048)

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**Author:** [@ANasc](https://discourse.julialang.org/u/ANasc)\
**Replies:** 7\
**Last updated:** [July 10, 2019, 1:15pm UTC](https://discourse.julialang.org/t/declaring-state-dependent-delay-with-ddeproblem-simulation-gets-slower/26048 "2019-07-10T13:15:33Z")

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Dear All, I am having a hard time figuring out how to declare dependent\_lags that depend on one of the state variables in my DDE model (using DelayDiffEq.jl). It seems like it should be easy since the state variable i…

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## [Chaostools reinit! function](https://discourse.julialang.org/t/chaostools-reinit-function/26046)

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**Author:** [@jamblejoe](https://discourse.julialang.org/u/jamblejoe)\
**Replies:** 11\
**Last updated:** [July 7, 2019, 10:50pm UTC](https://discourse.julialang.org/t/chaostools-reinit-function/26046 "2019-07-07T22:50:38Z")

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Hi, so I am calculating Lyapunov exponents for a lot of initial values, parameters for specific systems. I want to make heavy use of the reinit! function for integrator objects, especially the tangent\_integrator from th…

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## [Spiking Neural Network](https://discourse.julialang.org/t/spiking-neural-network/24908)

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**Author:** [@grero](https://discourse.julialang.org/u/grero)\
**Replies:** 5\
**Last updated:** [June 4, 2019, 11:36pm UTC](https://discourse.julialang.org/t/spiking-neural-network/24908 "2019-06-04T23:36:42Z")

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Hi, I am trying to implement the spiking neural network model in this paper https://www.frontiersin.org/articles/10.3389/fninf.2018.00079/full and I wanted to use DifferentialEquations.jl Basically, the model consists o…

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## [Monte Carlo problem (distributed computing, DifferentialEquations pkg) with ForwardDiff AD for parameter estimation](https://discourse.julialang.org/t/monte-carlo-problem-distributed-computing-differentialequations-pkg-with-forwarddiff-ad-for-parameter-estimation/24697)

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**Author:** [@moesphere](https://discourse.julialang.org/u/moesphere)\
**Replies:** 1\
**Last updated:** [May 28, 2019, 4:41pm UTC](https://discourse.julialang.org/t/monte-carlo-problem-distributed-computing-differentialequations-pkg-with-forwarddiff-ad-for-parameter-estimation/24697 "2019-05-28T16:41:44Z")

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I am trying to use a Monte Carlo problem (distributed computing) from the Differential Equations package for parameter estimation using AD from ForwardDiff. It is working when I define the objective function directly in…

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## [Code optimization a (simple) advection difference scheme](https://discourse.julialang.org/t/code-optimization-a-simple-advection-difference-scheme/24532)

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**Author:** [@fdevuyst](https://discourse.julialang.org/u/fdevuyst)\
**Replies:** 2\
**Last updated:** [May 23, 2019, 6:43pm UTC](https://discourse.julialang.org/t/code-optimization-a-simple-advection-difference-scheme/24532 "2019-05-23T18:43:50Z")

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Hi, I’m beginner in Julia. I tried a simple code, but was a little bit disappointed with the performance. Could you give me hints in optimizing this snippet ? Kind regards, Florian 2D advection equation, periodic boun…

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## [Lagrange Interpolation Function Generator](https://discourse.julialang.org/t/lagrange-interpolation-function-generator/3427)

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**Author:** [@anodos](https://discourse.julialang.org/u/anodos)\
**Replies:** 3\
**Last updated:** [May 22, 2019, 10:31pm UTC](https://discourse.julialang.org/t/lagrange-interpolation-function-generator/3427 "2019-05-22T22:31:59Z")

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I couldn’t find an implementation of Lagrange Interpolation in Julia, so built my own. This function simply takes a set of points, as stored in the two vectors xvals and yvals, and spits out the Lagrange Polynomial that …

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## [Monte Carlo problem, saving at different time points with 'saveat' from DifferentialEquations pkg](https://discourse.julialang.org/t/monte-carlo-problem-saving-at-different-time-points-with-saveat-from-differentialequations-pkg/24476)

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**Author:** [@moesphere](https://discourse.julialang.org/u/moesphere)\
**Replies:** 1\
**Last updated:** [May 22, 2019, 2:17pm UTC](https://discourse.julialang.org/t/monte-carlo-problem-saving-at-different-time-points-with-saveat-from-differentialequations-pkg/24476 "2019-05-22T14:17:51Z")

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Is it possible to save at different time points for each ODE problem in a Monte Carlo study? DifferentialEquations.solve(MCprob, saveat=\[10.0,20.0\]) works fine, but saves each ODE problem at the same time points. I am…

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## [How to load URDF files with .dae models into MeshCat?](https://discourse.julialang.org/t/how-to-load-urdf-files-with-dae-models-into-meshcat/19509)

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**Author:** [@cserteGT3](https://discourse.julialang.org/u/cserteGT3)\
**Replies:** 11\
**Last updated:** [May 15, 2019, 6:54am UTC](https://discourse.julialang.org/t/how-to-load-urdf-files-with-dae-models-into-meshcat/19509 "2019-05-15T06:54:13Z")

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I’m trying to use the JuliaRobotics ecosystem with UR robotic arms and can not find a way to open the official URDF-s. My problem is, that .dae files are not supported, and if I convert those files to .obj, then the mode…

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## [NetLogo Julia extension](https://discourse.julialang.org/t/netlogo-julia-extension/24023)

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**Author:** [@sbacelar](https://discourse.julialang.org/u/sbacelar)\
**Replies:** 4\
**Last updated:** [May 10, 2019, 10:40am UTC](https://discourse.julialang.org/t/netlogo-julia-extension/24023 "2019-05-10T10:40:45Z")

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Just a suggestion. NetLogo has R , Python and Mathematica extensions. why not create a Julia extension?

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## [Issue with DSP.Util.hilbert](https://discourse.julialang.org/t/issue-with-dsp-util-hilbert/23842)

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**Author:** [@koenigjaeger](https://discourse.julialang.org/u/koenigjaeger)\
**Replies:** 1\
**Last updated:** [May 4, 2019, 7:15am UTC](https://discourse.julialang.org/t/issue-with-dsp-util-hilbert/23842 "2019-05-04T07:15:16Z")

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I was looking to get the envelope of a signal and looking at the example at Discrete-time analytic signal using Hilbert transform - MATLAB hilbert and checking this in octave using the signal package from forge I am gett…

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## [Robotics - SensorFeatureTracking](https://discourse.julialang.org/t/robotics-sensorfeaturetracking/23436)

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**Author:** [@johnh](https://discourse.julialang.org/u/johnh)\
**Replies:** 2\
**Last updated:** [April 23, 2019, 12:32pm UTC](https://discourse.julialang.org/t/robotics-sensorfeaturetracking/23436 "2019-04-23T12:32:30Z")

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The package in Julia Robotics for feature tracking seems to be a bit neglected. Is there anything equivalent which is more active?

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## [Time-dependent events in ODE](https://discourse.julialang.org/t/time-dependent-events-in-ode/14951)

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**Author:** [@hellopascal](https://discourse.julialang.org/u/hellopascal)\
**Replies:** 14\
**Last updated:** [April 20, 2019, 2:52am UTC](https://discourse.julialang.org/t/time-dependent-events-in-ode/14951 "2019-04-20T02:52:20Z")

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I recently started with Julia and wanted to implement one of my usual problems - implement time-depended events. For now I have: # Packages using Plots using DifferentialEquations # Parameters k21 = 0.14\*24 k12 = 0.06…

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## [Project PyCX in Julia](https://discourse.julialang.org/t/project-pycx-in-julia/23305)

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**Author:** [@sbacelar](https://discourse.julialang.org/u/sbacelar)\
**Replies:** 2\
**Last updated:** [April 19, 2019, 1:57pm UTC](https://discourse.julialang.org/t/project-pycx-in-julia/23305 "2019-04-19T13:57:45Z")

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Just a suggestion by a Complexity Science student and a Julia fan (not knowing enough): to build a Julia version of Project PyCX in Julia. Hiroki Sayama, Introduction to the Modeling and Analysis of Complex Systems uses…

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## [RigidBodyDynamics : velocity\_range](https://discourse.julialang.org/t/rigidbodydynamics-velocity-range/23004)

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**Author:** [@RogerP](https://discourse.julialang.org/u/RogerP)\
**Replies:** 2\
**Last updated:** [April 11, 2019, 7:28am UTC](https://discourse.julialang.org/t/rigidbodydynamics-velocity-range/23004 "2019-04-11T07:28:46Z")

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I am trying to understand the relationship between v and q̇ using the functions that provide the Jacobians relating the two and I wonder if someone could explain the meaning of the required velocity ranges? The docs say…

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## [ForwardDiff for functions of several (vector) variables?](https://discourse.julialang.org/t/forwarddiff-for-functions-of-several-vector-variables/22918)

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**Author:** [@zdenek\_hurak](https://discourse.julialang.org/u/zdenek_hurak)\
**Replies:** 2\
**Last updated:** [April 10, 2019, 1:42pm UTC](https://discourse.julialang.org/t/forwarddiff-for-functions-of-several-vector-variables/22918 "2019-04-10T13:42:17Z")

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Is it possible to use ForwardDiff for functions of several variables? In particular, consider a scalar function L(x,u) of two vector variables x and u. I want to compute the gradient of L() with respect to x. From the d…

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## [How to define state-dependent delay in delayed differential equations solver in Julia?](https://discourse.julialang.org/t/how-to-define-state-dependent-delay-in-delayed-differential-equations-solver-in-julia/18007)

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**Author:** [@PeterXG](https://discourse.julialang.org/u/PeterXG)\
**Replies:** 1\
**Last updated:** [November 27, 2018, 7:34am UTC](https://discourse.julialang.org/t/how-to-define-state-dependent-delay-in-delayed-differential-equations-solver-in-julia/18007 "2018-11-27T07:34:20Z")

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Dear All, I’m transferring from Matlab to Julia to solve delayed differential equations. I read documentation and notice it says define state-dependent delay by prob = DDEProblem(bc\_model,u0,h,tspan; dependent\_lags = …

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## [Help with hyper-stiff ODE system](https://discourse.julialang.org/t/help-with-hyper-stiff-ode-system/22681)

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**Author:** [@jcook](https://discourse.julialang.org/u/jcook)\
**Replies:** 2\
**Last updated:** [April 3, 2019, 10:22am UTC](https://discourse.julialang.org/t/help-with-hyper-stiff-ode-system/22681 "2019-04-03T10:22:19Z")

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Dear All, I’ve come against a pretty tricky problem that I can’t find an accurate and performant solution to in Julia. There is a closed source FORTRAN code that can solve this problem quickly and accurately. So at leas…

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## [Forward differentiation and differential equations with solvers like LSODA, Sundials etc](https://discourse.julialang.org/t/forward-differentiation-and-differential-equations-with-solvers-like-lsoda-sundials-etc/22371)

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**Author:** [@mzhenirovskyy](https://discourse.julialang.org/u/mzhenirovskyy)\
**Replies:** 2\
**Last updated:** [March 26, 2019, 8:03pm UTC](https://discourse.julialang.org/t/forward-differentiation-and-differential-equations-with-solvers-like-lsoda-sundials-etc/22371 "2019-03-26T20:03:28Z")

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I have similar questions to this thread I do explicit type conversion. When I use “standard” solver like Tsit5() everything is OK. But with solvers like lsoda() or CVODE\_BDF() I’m getting an error: Example: using Dif…

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## [RigidBodyDynamics, Munthe-Kaas integrator, step(integrator, t, Δt)](https://discourse.julialang.org/t/rigidbodydynamics-munthe-kaas-integrator-step-integrator-t-t/21906)

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**Author:** [@RogerP](https://discourse.julialang.org/u/RogerP)\
**Replies:** 4\
**Last updated:** [March 18, 2019, 8:49am UTC](https://discourse.julialang.org/t/rigidbodydynamics-munthe-kaas-integrator-step-integrator-t-t/21906 "2019-03-18T08:49:00Z")

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I want to set up a stepwise Munthe-Kass integrator for use in a real-time control system. I do: t = 0.0; Δt = 1e-4 ringBuff2 = RigidBodyDynamics.OdeIntegrators.RingBufferStorage{Float64}(state, 10000) butcherTableau = R…

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## [Simulating a Mars Rover - How can I account for random horizontal wind speeds?](https://discourse.julialang.org/t/simulating-a-mars-rover-how-can-i-account-for-random-horizontal-wind-speeds/21642)

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**Author:** [@Rilind\_Berisha](https://discourse.julialang.org/u/Rilind_Berisha)\
**Replies:** 0\
**Last updated:** [March 8, 2019, 5:46pm UTC](https://discourse.julialang.org/t/simulating-a-mars-rover-how-can-i-account-for-random-horizontal-wind-speeds/21642 "2019-03-08T17:46:23Z")

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Hi, This is my first post on here. I’m currently working on a small project to generate and plot a Mars Rover landing. I’ve figured out how code an autopilot that allows me to land on a flat surface at a safe vertical s…

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## [Generating high-dimensional Sobol sequences](https://discourse.julialang.org/t/generating-high-dimensional-sobol-sequences/21521)

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**Author:** [@jocklawrie](https://discourse.julialang.org/u/jocklawrie)\
**Replies:** 2\
**Last updated:** [March 7, 2019, 4:54am UTC](https://discourse.julialang.org/t/generating-high-dimensional-sobol-sequences/21521 "2019-03-07T04:54:42Z")

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Hi there, I am using Sobol sequences to generate say 10,000 draws from the Multivariate Normal with dimension 100, mean vector 0 and covariance matrix equal to the identity matrix. Generating the sequence is fine, but …

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## [Is there any microsimulation package in Julia?](https://discourse.julialang.org/t/is-there-any-microsimulation-package-in-julia/20049)

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**Author:** [@sbacelar](https://discourse.julialang.org/u/sbacelar)\
**Replies:** 4\
**Last updated:** [February 27, 2019, 11:26pm UTC](https://discourse.julialang.org/t/is-there-any-microsimulation-package-in-julia/20049 "2019-02-27T23:26:08Z")

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Something along the lines of LIAM2 in Python or MicSim in R.

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## [Use Symplectic Integrator for ODE for time reversability constraint](https://discourse.julialang.org/t/use-symplectic-integrator-for-ode-for-time-reversability-constraint/20955)

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**Author:** [@mleprovost](https://discourse.julialang.org/u/mleprovost)\
**Replies:** 6\
**Last updated:** [February 21, 2019, 8:39pm UTC](https://discourse.julialang.org/t/use-symplectic-integrator-for-ode-for-time-reversability-constraint/20955 "2019-02-21T20:39:59Z")

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Hi everyone, I would like to use Symplectic Integrators such as VelocityVerlet or VerletLeapfrog from DifferentialEquations.jl to ensure the time-reversibility of the equation of motion. Nonetheless, my problem can no…

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