# Modelling & Simulations

**URL:** https://discourse.julialang.org/c/domain/models/21.md?page=63

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**Page:** 64

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## [User-defined outputs in DifferentialEquations](https://discourse.julialang.org/t/user-defined-outputs-in-differentialequations/20754)

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**Author:** [@asprionj](https://discourse.julialang.org/u/asprionj)\
**Replies:** 3\
**Last updated:** [February 13, 2019, 4:34pm UTC](https://discourse.julialang.org/t/user-defined-outputs-in-differentialequations/20754 "2019-02-13T16:34:54Z")

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Hi, is there a possibility to specify outputs that are recorded along the state variables when running a simulation in DifferentialEquations? I could not find anything relating to this in the documentation… Of course, I…

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## [Uncertainties in DiffEqFlux.jl](https://discourse.julialang.org/t/uncertainties-in-diffeqflux-jl/20660)

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**Author:** [@spinkney](https://discourse.julialang.org/u/spinkney)\
**Replies:** 2\
**Last updated:** [February 11, 2019, 9:40pm UTC](https://discourse.julialang.org/t/uncertainties-in-diffeqflux-jl/20660 "2019-02-11T21:40:51Z")

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I watched the JuliaCon 2018 | PuMaS.jl: Pharmaceutical Modeling and Simulation Engine given by @ChrisRackauckas and saw the part about propagation of parameter uncertainties around 21:47. A (possibly) quick question reg…

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## [DOOM fire animation](https://discourse.julialang.org/t/doom-fire-animation/19100)

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**Author:** [@gdkrmr](https://discourse.julialang.org/u/gdkrmr)\
**Replies:** 4\
**Last updated:** [December 31, 2018, 12:42pm UTC](https://discourse.julialang.org/t/doom-fire-animation/19100 "2018-12-31T12:42:19Z")

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Just for fun, I recreated the fire animation from DOOM in Julia: https://gist.github.com/gdkrmr/ea4e7259f58e1504dbc46538dc4ad0e5 Code was adapted from here: http://fabiensanglard.net/doom\_fire\_psx/

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## [RigidBodyDynamics URDF inertia values](https://discourse.julialang.org/t/rigidbodydynamics-urdf-inertia-values/18384)

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**Author:** [@RogerP](https://discourse.julialang.org/u/RogerP)\
**Replies:** 3\
**Last updated:** [December 8, 2018, 3:38am UTC](https://discourse.julialang.org/t/rigidbodydynamics-urdf-inertia-values/18384 "2018-12-08T03:38:42Z")

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I am building my models directly from a relational database and the RigidBody components are loaded with those inertia values. (I can simply call up different configurations of robot arm with various numbers of links/joi…

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## [Differential equation solver example gives an error: MethodError: no method matching OrdinaryDiffEq.DEOptions](https://discourse.julialang.org/t/differential-equation-solver-example-gives-an-error-methoderror-no-method-matching-ordinarydiffeq-deoptions/18001)

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**Author:** [@PeterXG](https://discourse.julialang.org/u/PeterXG)\
**Replies:** 6\
**Last updated:** [December 3, 2018, 12:32pm UTC](https://discourse.julialang.org/t/differential-equation-solver-example-gives-an-error-methoderror-no-method-matching-ordinarydiffeq-deoptions/18001 "2018-12-03T12:32:48Z")

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Dear All, I run the sample code to solve a differential equation from tutorial. const p0 = 0.2; const q0 = 0.3; const v0 = 1; const d0 = 5 const p1 = 0.2; const q1 = 0.3; const v1 = 1; const d1 = 1 const d2 = 1; const …

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## [Difficulties with DifferentialEquations package](https://discourse.julialang.org/t/difficulties-with-differentialequations-package/18204)

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**Author:** [@BLI](https://discourse.julialang.org/u/BLI)\
**Replies:** 13\
**Last updated:** [December 2, 2018, 9:14pm UTC](https://discourse.julialang.org/t/difficulties-with-differentialequations-package/18204 "2018-12-02T21:14:33Z")

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I’m testing the DifferentialEquations package on a model I developed ca. 1993 (just dug it of the archives…). I try to simulate 5 Argon molecules bouncing around in 2D, locked up between “Lennard-Jones” like potential wa…

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## [submit a Bug report when using SCS solver](https://discourse.julialang.org/t/submit-a-bug-report-when-using-scs-solver/18080)

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**Author:** [@Ryan](https://discourse.julialang.org/u/Ryan)\
**Replies:** 2\
**Last updated:** [November 28, 2018, 12:45am UTC](https://discourse.julialang.org/t/submit-a-bug-report-when-using-scs-solver/18080 "2018-11-28T00:45:48Z")

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bug report when using SCS solver Please submit a bug report with steps to reproduce this fault, and any error messages that follow (i n their entirety). Thanks. Exception: EXCEPTION\_ACCESS\_VIOLATION at 0x6669d61c – va…

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## [Constraints in RigidBodyDynamics](https://discourse.julialang.org/t/constraints-in-rigidbodydynamics/18010)

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**Author:** [@RogerP](https://discourse.julialang.org/u/RogerP)\
**Replies:** 2\
**Last updated:** [November 26, 2018, 3:53pm UTC](https://discourse.julialang.org/t/constraints-in-rigidbodydynamics/18010 "2018-11-26T15:53:19Z")

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Is there a way of adding kinematic constraints using RBD? For instance, I have a double-prismatic joint, i.e a telescopic joint, where the inner always moves at twice the speed of the outer. (The two components are huge …

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## [ControlSystems - MIMO inverse / MIMO feedback loops](https://discourse.julialang.org/t/controlsystems-mimo-inverse-mimo-feedback-loops/17784)

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**Author:** [@silch12](https://discourse.julialang.org/u/silch12)\
**Replies:** 3\
**Last updated:** [November 21, 2018, 4:58pm UTC](https://discourse.julialang.org/t/controlsystems-mimo-inverse-mimo-feedback-loops/17784 "2018-11-21T16:58:26Z")

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Hi there. I’m currently studying Electrical Engineering and we have now a lecture Control Systems. Since we (should) use Matlab at school, but I can’t come to terms with proprietary software, I came across Julia as an …

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## [RigidBodyDynamics.jl attaching a new rigid body to the system](https://discourse.julialang.org/t/rigidbodydynamics-jl-attaching-a-new-rigid-body-to-the-system/17451)

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**Author:** [@phelipe](https://discourse.julialang.org/u/phelipe)\
**Replies:** 4\
**Last updated:** [November 18, 2018, 3:11pm UTC](https://discourse.julialang.org/t/rigidbodydynamics-jl-attaching-a-new-rigid-body-to-the-system/17451 "2018-11-18T15:11:35Z")

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Is it possible to add an extra load to a mechanism created from an urdf? For example, add a sphere to the last joint of a system. Can RigidBodyDynamics.attach! be used for this?

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## [Great news for Dynamics in Julia!](https://discourse.julialang.org/t/great-news-for-dynamics-in-julia/17321)

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**Author:** [@Datseris](https://discourse.julialang.org/u/Datseris)\
**Replies:** 1\
**Last updated:** [November 8, 2018, 8:18pm UTC](https://discourse.julialang.org/t/great-news-for-dynamics-in-julia/17321 "2018-11-08T20:18:16Z")

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Hello everyone, Since I don’t have a blog, this is like an announcement of shorts for JuliaDynamics. I bear good news :slight\_smile: DSWeb prize Pretty much everyone is aware of this, but I just want to apologize for n…

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## [Geometric ray tracing](https://discourse.julialang.org/t/geometric-ray-tracing/17182)

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**Author:** [@yakir12](https://discourse.julialang.org/u/yakir12)\
**Replies:** 2\
**Last updated:** [November 5, 2018, 10:40pm UTC](https://discourse.julialang.org/t/geometric-ray-tracing/17182 "2018-11-05T22:40:55Z")

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Is there anyone out there that is both semi-versed in geometric ray tracing and wants to write a good ray tracing library? To be clear, I’m not talking about ray tracing in graphics but more about ray tracing in physics,…

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## [How to store joint transform while running simulation in RigidBodyDynamics.jl](https://discourse.julialang.org/t/how-to-store-joint-transform-while-running-simulation-in-rigidbodydynamics-jl/16797)

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**Author:** [@HiroIshida](https://discourse.julialang.org/u/HiroIshida)\
**Replies:** 5\
**Last updated:** [October 31, 2018, 1:54am UTC](https://discourse.julialang.org/t/how-to-store-joint-transform-while-running-simulation-in-rigidbodydynamics-jl/16797 "2018-10-31T01:54:48Z")

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Does anyone know how to store joint transform while running a simulation in RigidBodyDynamics.jl? I know that getting a joint transform before and after simulate() by using joint\_transform(). But, I don’t know how to do …

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## [RigidBodySim.jl and disturbances](https://discourse.julialang.org/t/rigidbodysim-jl-and-disturbances/16576)

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**Author:** [@phelipe](https://discourse.julialang.org/u/phelipe)\
**Replies:** 5\
**Last updated:** [October 26, 2018, 1:57pm UTC](https://discourse.julialang.org/t/rigidbodysim-jl-and-disturbances/16576 "2018-10-26T13:57:29Z")

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Hi, is there any way to add friction or other disturbance to the model as the controller is added? Something like: closed\_loop\_dynamics = Dynamics(robot, control!, disturbance!)

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## [Setting gravity in RigidBodyDynamics.jl](https://discourse.julialang.org/t/setting-gravity-in-rigidbodydynamics-jl/16748)

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**Author:** [@HiroIshida](https://discourse.julialang.org/u/HiroIshida)\
**Replies:** 2\
**Last updated:** [October 25, 2018, 6:30am UTC](https://discourse.julialang.org/t/setting-gravity-in-rigidbodydynamics-jl/16748 "2018-10-25T06:30:59Z")

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I have just started to use RigidBodyDynamics. According to the tutorial, the proper way to set gravity seems m = Mechanism(world; gravity = SVector(0, 0, g). But when constructing a mechanism using parse\_urdf, what is t…

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## ["using Plots" suddenly stopped working](https://discourse.julialang.org/t/using-plots-suddenly-stopped-working/16695)

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**Author:** [@Torkel](https://discourse.julialang.org/u/Torkel)\
**Replies:** 2\
**Last updated:** [October 23, 2018, 4:47pm UTC](https://discourse.julialang.org/t/using-plots-suddenly-stopped-working/16695 "2018-10-23T16:47:42Z")

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I have been using Plots in Julia 1.0 for a whil now and it all worked ok. However, I needed some plots were I more easily could customize various things (line thickness etc.) to make a pretty figure and I thought I shoul…

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## [ControlSystems & LTI structure?](https://discourse.julialang.org/t/controlsystems-lti-structure/16653)

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**Author:** [@BLI](https://discourse.julialang.org/u/BLI)\
**Replies:** 2\
**Last updated:** [October 23, 2018, 6:46am UTC](https://discourse.julialang.org/t/controlsystems-lti-structure/16653 "2018-10-23T06:46:22Z")

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I haven’t delved deeply into Julia types/structs, and am curious about the LTI structure… It appears to me that LTI is defined for finite dimensional systems only, i.e., no time delay, etc. What is the internal storage…

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## [When solving non-diagonal noise SDE: Function g called twice in each timestep, changing u inbetween?](https://discourse.julialang.org/t/when-solving-non-diagonal-noise-sde-function-g-called-twice-in-each-timestep-changing-u-inbetween/15618)

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**Author:** [@Torkel](https://discourse.julialang.org/u/Torkel)\
**Replies:** 2\
**Last updated:** [September 28, 2018, 9:39pm UTC](https://discourse.julialang.org/t/when-solving-non-diagonal-noise-sde-function-g-called-twice-in-each-timestep-changing-u-inbetween/15618 "2018-09-28T21:39:23Z")

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In short: When making solving SDEs the noise function seems to be called twice in every timestep, with the variable values being changed in between. This causes out of domain errors when my positive\_domain callback canno…

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## [ControlSystems: dlqr method](https://discourse.julialang.org/t/controlsystems-dlqr-method/15217)

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**Author:** [@BLI](https://discourse.julialang.org/u/BLI)\
**Replies:** 1\
**Last updated:** [September 20, 2018, 7:47am UTC](https://discourse.julialang.org/t/controlsystems-dlqr-method/15217 "2018-09-20T07:47:10Z")

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I’m a little confused by the “docstring”/documentation of dlqr: dlqr(A, B, Q, R), dlqr(sys, Q, R) Calculate the optimal gain matrix K for the state-feedback law u\[k\] = K\*x\[k\] that minimizes the cost function: J …

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## [ControlSystems -- root locus, etc.?](https://discourse.julialang.org/t/controlsystems-root-locus-etc/14706)

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**Author:** [@BLI](https://discourse.julialang.org/u/BLI)\
**Replies:** 14\
**Last updated:** [September 15, 2018, 3:36pm UTC](https://discourse.julialang.org/t/controlsystems-root-locus-etc/14706 "2018-09-15T15:36:53Z")

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I was just playing around with the ControlSystems package. One question and one observation… Q: is there a function for plotting root locus? Of course, it is easy to do this in a for loop, but if there is a function, my…

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## [Is there any example of porting an octave multi compartment PBPK ode model to Julia?](https://discourse.julialang.org/t/is-there-any-example-of-porting-an-octave-multi-compartment-pbpk-ode-model-to-julia/14506)

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**Author:** [@mmarikar](https://discourse.julialang.org/u/mmarikar)\
**Replies:** 1\
**Last updated:** [September 4, 2018, 1:07am UTC](https://discourse.julialang.org/t/is-there-any-example-of-porting-an-octave-multi-compartment-pbpk-ode-model-to-julia/14506 "2018-09-04T01:07:42Z")

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I was able to get a single compartment model working as indicated below using Chris R’s links. My example can be seen at https://github.com/mmarikar/julia/blob/master/OneCompartmentPBPKmodel.jl Does anyone have an exam…

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## [Slight change in an equation brings Domain error with mcpSolve](https://discourse.julialang.org/t/slight-change-in-an-equation-brings-domain-error-with-mcpsolve/13881)

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**Author:** [@axelle](https://discourse.julialang.org/u/axelle)\
**Replies:** 0\
**Last updated:** [August 22, 2018, 1:04pm UTC](https://discourse.julialang.org/t/slight-change-in-an-equation-brings-domain-error-with-mcpsolve/13881 "2018-08-22T13:04:51Z")

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Good afternoon, I have a system of equations and keep getting “domain error” for some values of the parameters. I have been able to solve a lot of them. For instance, I had some difficulties with some integral that were…

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## [Calculating bandstructure of graphene](https://discourse.julialang.org/t/calculating-bandstructure-of-graphene/13766)

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**Author:** [@Janis\_Erdmanis](https://discourse.julialang.org/u/Janis_Erdmanis)\
**Replies:** 24\
**Last updated:** [August 22, 2018, 8:38pm UTC](https://discourse.julialang.org/t/calculating-bandstructure-of-graphene/13766 "2018-08-22T20:38:02Z")

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Looking on github I see that there are some packages in Julia which are tagged with density functional theory (DFT). I wonder, if any of them can be used for calculating band-structure of graphene (for example figure 3 i…

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## [System Dynamics packages](https://discourse.julialang.org/t/system-dynamics-packages/8222)

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**Author:** [@smldis](https://discourse.julialang.org/u/smldis)\
**Replies:** 12\
**Last updated:** [August 12, 2018, 8:21pm UTC](https://discourse.julialang.org/t/system-dynamics-packages/8222 "2018-08-12T20:21:52Z")

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Continuing the discussion from this post in 1.0 adoption path?: System dynamics ecosystem in julia needs coordination and development efforts. If anybody wants to discuss in this post I am kind of interested too. @jlper…

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## [Clean Numerical Simulation (Taylor Series Method)](https://discourse.julialang.org/t/clean-numerical-simulation-taylor-series-method/12893)

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**Author:** [@m4r35n357](https://discourse.julialang.org/u/m4r35n357)\
**Replies:** 9\
**Last updated:** [August 12, 2018, 1:41pm UTC](https://discourse.julialang.org/t/clean-numerical-simulation-taylor-series-method/12893 "2018-08-12T13:41:30Z")

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Hi all, very new to Julia, and not in academia BTW. I have been investigating the opinions and findings in this paper, and I thought I would contribute some Julia code which performs the aforementioned simulation to pot…

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## [Model solving - method error using NLsolve](https://discourse.julialang.org/t/model-solving-method-error-using-nlsolve/13035)

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**Author:** [@axelle](https://discourse.julialang.org/u/axelle)\
**Replies:** 15\
**Last updated:** [August 10, 2018, 9:12am UTC](https://discourse.julialang.org/t/model-solving-method-error-using-nlsolve/13035 "2018-08-10T09:12:14Z")

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Hi, I am stuck with a code (solving an economic model) and would need some help. I am sorry if the mistake is obvious, but I am new to this and would really need some help there. I have the following code: function bk\_o…

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## [ANN: MetaFields.jl and Flatten.jl - packages for writing composable models](https://discourse.julialang.org/t/ann-metafields-jl-and-flatten-jl-packages-for-writing-composable-models/12849)

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**Author:** [@Raf](https://discourse.julialang.org/u/Raf)\
**Replies:** 10\
**Last updated:** [August 7, 2018, 10:14am UTC](https://discourse.julialang.org/t/ann-metafields-jl-and-flatten-jl-packages-for-writing-composable-models/12849 "2018-08-07T10:14:35Z")

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I’ve been putting together a few biophysical models over the last year, and have constantly encountered what I feel to be the core software problem in my field: sharing high performance code in general ways never happens…

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## [Julia interface to Bullet Physics?](https://discourse.julialang.org/t/julia-interface-to-bullet-physics/12617)

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**Author:** [@jbrea](https://discourse.julialang.org/u/jbrea)\
**Replies:** 19\
**Last updated:** [August 6, 2018, 8:42am UTC](https://discourse.julialang.org/t/julia-interface-to-bullet-physics/12617 "2018-08-06T08:42:49Z")

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I came across the Bullet Physics SDK and was impressed by the rich collection of examples. Now I wonder: Is anybody interested in a Julia interface to the Bullet Physics SDK? Did somebody already start working on this? …

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## [ControlSystems / Frequency in Hz for bodeplot](https://discourse.julialang.org/t/controlsystems-frequency-in-hz-for-bodeplot/12683)

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**Author:** [@Patrick\_Dubus](https://discourse.julialang.org/u/Patrick_Dubus)\
**Replies:** 9\
**Last updated:** [July 30, 2018, 3:31pm UTC](https://discourse.julialang.org/t/controlsystems-frequency-in-hz-for-bodeplot/12683 "2018-07-30T15:31:50Z")

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Hello, I would like to know how to change the xaxis unit (rad/s) to frequency for bodeplot. Thanks in advance. Patrick.

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## [Error solving ODE - Integrator stepped past tstops](https://discourse.julialang.org/t/error-solving-ode-integrator-stepped-past-tstops/12303)

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**Author:** [@mariepied](https://discourse.julialang.org/u/mariepied)\
**Replies:** 4\
**Last updated:** [July 11, 2018, 5:03pm UTC](https://discourse.julialang.org/t/error-solving-ode-integrator-stepped-past-tstops/12303 "2018-07-11T17:03:28Z")

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I get a error when solving a differential equation with the DifferentialEquations package. The error appear or not depending on the seed i’m specifying. I can’t understand from where this error come from, i’m not sure if…

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