# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?no_subcategories=false&page=261

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**Page:** 262

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## [Question about low pass filter in DSP.jl](https://discourse.julialang.org/t/question-about-low-pass-filter-in-dsp-jl/79214)

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**Author:** [@henry2004y](https://discourse.julialang.org/u/henry2004y)\
**Replies:** 5\
**Last updated:** [August 3, 2022, 10:00am UTC](https://discourse.julialang.org/t/question-about-low-pass-filter-in-dsp-jl/79214 "2022-08-03T10:00:16Z")

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Hi, I’m new to the domain of signal processing. Recently I have encountered some phase related issues with the low pass filter in DSP.jl. In MATLAB, fs = 1e3; t = 0:1/fs:1; % comment out random noise for testing x = \[…

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## [Is it necessary to add GR.jl?](https://discourse.julialang.org/t/is-it-necessary-to-add-gr-jl/85217)

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**Author:** [@vitaminace33](https://discourse.julialang.org/u/vitaminace33)\
**Replies:** 3\
**Last updated:** [August 3, 2022, 8:48am UTC](https://discourse.julialang.org/t/is-it-necessary-to-add-gr-jl/85217 "2022-08-03T08:48:13Z")

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GR is the default backend for plotting and works out of the box. Hence, the question, is it necessary to add GR.jl via Pkg.add? Would this add any extra capabilities to plotting?

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## [Can not choose alg for lyapunovspectrum DynamicalSystems.jl](https://discourse.julialang.org/t/can-not-choose-alg-for-lyapunovspectrum-dynamicalsystems-jl/85173)

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**Author:** [@Sergey\_Novak](https://discourse.julialang.org/u/Sergey_Novak)\
**Replies:** 9\
**Last updated:** [August 3, 2022, 7:46am UTC](https://discourse.julialang.org/t/can-not-choose-alg-for-lyapunovspectrum-dynamicalsystems-jl/85173 "2022-08-03T07:46:32Z")

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I have system and parametres: function HR!(du, u, p, t) function sigma(x) return 1.0 / ( 1.0 + exp( -10.0 \* ( x - ( - 0.25 ) ) ) ) end a, b, c, d, s, xr, r, I, vs, k1, k2, el\_link = …

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## [Dirac Delta with DifferentialEquations.jl](https://discourse.julialang.org/t/dirac-delta-with-differentialequations-jl/84835)

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**Author:** [@cmdenis](https://discourse.julialang.org/u/cmdenis)\
**Replies:** 4\
**Last updated:** [August 2, 2022, 8:18pm UTC](https://discourse.julialang.org/t/dirac-delta-with-differentialequations-jl/84835 "2022-08-02T20:18:55Z")

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Hi, I want to integrate a differential equations system numerically, but some equations involve Dirac delta functions. Is there a built-in delta function to do this? Or should I be mimicking one with a continuous funct…

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## [How can I change a single color in a Plots.jl palette?](https://discourse.julialang.org/t/how-can-i-change-a-single-color-in-a-plots-jl-palette/85172)

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**Author:** [@thompsonmj](https://discourse.julialang.org/u/thompsonmj)\
**Replies:** 4\
**Last updated:** [August 2, 2022, 4:04pm UTC](https://discourse.julialang.org/t/how-can-i-change-a-single-color-in-a-plots-jl-palette/85172 "2022-08-02T16:04:11Z")

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If I have a palette, is there some way to change the colors by index? c = palette(:tab10) c\[10\] = colorant"black" ERROR: MethodError: no method matching setindex!(::ColorPalette, ::RGB{N0f8}, ::Int64)

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## [Broadcasting an expression-evaluator function](https://discourse.julialang.org/t/broadcasting-an-expression-evaluator-function/85127)

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**Author:** [@RXGottlieb](https://discourse.julialang.org/u/RXGottlieb)\
**Replies:** 2\
**Last updated:** [August 2, 2022, 2:21pm UTC](https://discourse.julialang.org/t/broadcasting-an-expression-evaluator-function/85127 "2022-08-02T14:21:46Z")

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Hello, I have a symbolic expression that I’d like to evaluate a large number of times on a GPU. A few days ago I made a post about creating an evaluator function (see: the previous post), which led me to Symbolics.build…

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## [Linearizing ModelingToolkit ODESystem](https://discourse.julialang.org/t/linearizing-modelingtoolkit-odesystem/61387)

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**Author:** [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)\
**Replies:** 3\
**Last updated:** [August 2, 2022, 11:58am UTC](https://discourse.julialang.org/t/linearizing-modelingtoolkit-odesystem/61387 "2022-08-02T11:58:48Z")

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I am having my bi-monthly go at ModelingToolkit and have reached a point where I can create an ODESystem from ControlSystems.jl StateSpace and connect a few of those togeher and simulate, nice :slight\_smile: As a next s…

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## [Agent Based Modeling resources other than Agents.jl documentation](https://discourse.julialang.org/t/agent-based-modeling-resources-other-than-agents-jl-documentation/85035)

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**Author:** [@franfram](https://discourse.julialang.org/u/franfram)\
**Replies:** 2\
**Last updated:** [August 2, 2022, 8:39am UTC](https://discourse.julialang.org/t/agent-based-modeling-resources-other-than-agents-jl-documentation/85035 "2022-08-02T08:39:32Z")

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Hello everyone. I’m starting to use Agents.jl for a PhD project on animal movement and epidemiology. I was wondering if anyone knew of additional resources to learn other than those of Agents.jl. George Datseris youtu…

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## [Nested data structure with value by reference](https://discourse.julialang.org/t/nested-data-structure-with-value-by-reference/85147)

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**Author:** [@Thomberger](https://discourse.julialang.org/u/Thomberger)\
**Replies:** 0\
**Last updated:** [August 2, 2022, 8:24am UTC](https://discourse.julialang.org/t/nested-data-structure-with-value-by-reference/85147 "2022-08-02T08:24:54Z")

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I would like to have nested structure with minimum memory allocation. This would need passing data by reference but i’m not able to enforce that explicitly. I have a small number (i.e. 5) of different geometries. Each g…

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## [Is there any way to optimize array additions and multiplications with transposes?](https://discourse.julialang.org/t/is-there-any-way-to-optimize-array-additions-and-multiplications-with-transposes/80268)

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**Author:** [@Geositta](https://discourse.julialang.org/u/Geositta)\
**Replies:** 27\
**Last updated:** [August 2, 2022, 8:06am UTC](https://discourse.julialang.org/t/is-there-any-way-to-optimize-array-additions-and-multiplications-with-transposes/80268 "2022-08-02T08:06:32Z")

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The question is related to python - Optimizing array additions and multiplications with transposes - Stack Overflow Given A is an array, I want to evaluate sum += p(A) \* factor(p) where p is a permutation/transpose, fa…

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## [Are there any interesting visualization examples in Julia？](https://discourse.julialang.org/t/are-there-any-interesting-visualization-examples-in-julia/62661)

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**Author:** [@Wind](https://discourse.julialang.org/u/Wind)\
**Replies:** 16\
**Last updated:** [August 2, 2022, 5:37am UTC](https://discourse.julialang.org/t/are-there-any-interesting-visualization-examples-in-julia/62661 "2022-08-02T05:37:48Z")

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I found a web page with a lot of dazzling and interesting javascript visualization examples. It’s true that programming language is the best drawing tool. Since Julia is very fast and easy to use, I assume it can do a l…

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## [Should model matrix for nested factors be full-rank?](https://discourse.julialang.org/t/should-model-matrix-for-nested-factors-be-full-rank/84733)

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**Author:** [@PharmCat](https://discourse.julialang.org/u/PharmCat)\
**Replies:** 15\
**Last updated:** [August 1, 2022, 8:45pm UTC](https://discourse.julialang.org/t/should-model-matrix-for-nested-factors-be-full-rank/84733 "2022-08-01T20:45:00Z")

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In some cases when levels of one factor all “inside” levels of another we have not full-rank model matrix from StatsModels. For example - calssical bioequivlence crossover study (2X2) with factors: Var ~ Formulation + …

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## [Makie inconsistency between GLMakie output and saved mp4 output](https://discourse.julialang.org/t/makie-inconsistency-between-glmakie-output-and-saved-mp4-output/85112)

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**Author:** [@gottacatchenall](https://discourse.julialang.org/u/gottacatchenall)\
**Replies:** 0\
**Last updated:** [August 1, 2022, 6:37pm UTC](https://discourse.julialang.org/t/makie-inconsistency-between-glmakie-output-and-saved-mp4-output/85112 "2022-08-01T18:37:41Z")

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Hi, I’m running the following code to create an animation with two axes within a figure. using Makie, GLMakie using Distributions fig = Figure(resolution=(1600,800)) ax1 = Axis(fig\[1,1\], title="Sampling Locations"…

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## [Symbolics.jl | Lie series expansion for PDEs](https://discourse.julialang.org/t/symbolics-jl-lie-series-expansion-for-pdes/84885)

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**Author:** [@Audrius-St](https://discourse.julialang.org/u/Audrius-St)\
**Replies:** 2\
**Last updated:** [August 1, 2022, 7:43pm UTC](https://discourse.julialang.org/t/symbolics-jl-lie-series-expansion-for-pdes/84885 "2022-08-01T19:43:31Z")

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Hello, I’ve used Sympy for several years now and am interested in giving Symbolics.jl a go with an eye to switching over completely. I’ve previously used Sympy to solve systems of ODES using the symbolic Lie series met…

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## [Euler Equation Iteration to solve an Optimization problem](https://discourse.julialang.org/t/euler-equation-iteration-to-solve-an-optimization-problem/84135)

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**Author:** [@Albert\_Zevelev](https://discourse.julialang.org/u/Albert_Zevelev)\
**Replies:** 21\
**Last updated:** [August 1, 2022, 7:20pm UTC](https://discourse.julialang.org/t/euler-equation-iteration-to-solve-an-optimization-problem/84135 "2022-08-01T19:20:11Z")

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I would like to solve a simple/routine economics problem with Euler Equation Iteration. The following code works well: using Interpolations, Plots, LinearAlgebra # PolyBasis(K) = \[ones(size(K)) K K.^2\] PolyGetCoef…

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## [Plots.jl contour line colors](https://discourse.julialang.org/t/plots-jl-contour-line-colors/85084)

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**Author:** [@gideonsimpson](https://discourse.julialang.org/u/gideonsimpson)\
**Replies:** 3\
**Last updated:** [August 1, 2022, 6:40pm UTC](https://discourse.julialang.org/t/plots-jl-contour-line-colors/85084 "2022-08-01T18:40:09Z")

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When using contour (not contourf) with Plots.jl, is there a way to force all the contour lines to be a single fixed color?

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## [Modelling uncertainty propagation in forecasts 🔮](https://discourse.julialang.org/t/modelling-uncertainty-propagation-in-forecasts/85089)

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**Author:** [@agucova](https://discourse.julialang.org/u/agucova)\
**Replies:** 1\
**Last updated:** [August 1, 2022, 2:58pm UTC](https://discourse.julialang.org/t/modelling-uncertainty-propagation-in-forecasts/85089 "2022-08-01T14:58:21Z")

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Hi everyone, I’ve been playing with Causal, a business modeling platform which does automatic uncertainty calculations in forecasts. This works by allowing one to set model parameters in terms of ranges, which are real…

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## [Kriging on surface of sphere](https://discourse.julialang.org/t/kriging-on-surface-of-sphere/85058)

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**Author:** [@yakir12](https://discourse.julialang.org/u/yakir12)\
**Replies:** 5\
**Last updated:** [August 1, 2022, 1:47pm UTC](https://discourse.julialang.org/t/kriging-on-surface-of-sphere/85058 "2022-08-01T13:47:39Z")

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I have a few random points on a sphere’s surface and I’d like to interpolate and extrapolate those using kriging. But I’m getting artefacts in the result that look like an issue with the fact that the coordinates are sph…

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## [Vector to lists of indices grouped by key](https://discourse.julialang.org/t/vector-to-lists-of-indices-grouped-by-key/85050)

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**Author:** [@FireCrumb](https://discourse.julialang.org/u/FireCrumb)\
**Replies:** 9\
**Last updated:** [August 1, 2022, 11:00am UTC](https://discourse.julialang.org/t/vector-to-lists-of-indices-grouped-by-key/85050 "2022-08-01T11:00:46Z")

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Hi, I have a vector of numbers: (in reality much larger) arr = Vector{Int64}(\[6, 9, 9, 4, 1, 1, 2, 7, 8, 3\]) I want to be able to generate the list of indices for each value: \> p = pairs(arr) pairs(::Vector{Int64})(.…

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## [Makie.jl figure with broken axis](https://discourse.julialang.org/t/makie-jl-figure-with-broken-axis/85062)

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**Author:** [@Kevin\_Kleinbeck](https://discourse.julialang.org/u/Kevin_Kleinbeck)\
**Replies:** 3\
**Last updated:** [August 1, 2022, 7:09am UTC](https://discourse.julialang.org/t/makie-jl-figure-with-broken-axis/85062 "2022-08-01T07:09:05Z")

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I intend to create a figure with a broken Axis, which can be useful when the data range is relatively large but relevant details occur only close to the maximal / minimal values. For example, let’s say we want to create…

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## [GPU performance and switching from tabular to recurrent data format for Flux.jl](https://discourse.julialang.org/t/gpu-performance-and-switching-from-tabular-to-recurrent-data-format-for-flux-jl/84969)

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**Author:** [@JLDC](https://discourse.julialang.org/u/JLDC)\
**Replies:** 5\
**Last updated:** [August 1, 2022, 6:52am UTC](https://discourse.julialang.org/t/gpu-performance-and-switching-from-tabular-to-recurrent-data-format-for-flux-jl/84969 "2022-08-01T06:52:48Z")

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When training a recurrent network using Flux.jl, a dataset with K features, S samples, and a sequence length of L should take the form of a vector of length L where each element is a K × S matrix. Let’s say that I have …

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## [Ensemble simulations with random initial conditions that sum to a fixed value](https://discourse.julialang.org/t/ensemble-simulations-with-random-initial-conditions-that-sum-to-a-fixed-value/84951)

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**Author:** [@Dragolonth](https://discourse.julialang.org/u/Dragolonth)\
**Replies:** 6\
**Last updated:** [August 1, 2022, 6:51am UTC](https://discourse.julialang.org/t/ensemble-simulations-with-random-initial-conditions-that-sum-to-a-fixed-value/84951 "2022-08-01T06:51:59Z")

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Hi all. For my ensemble problem, I would like to randomize the initial conditions for each trajectory. However, I would like the sum of certain species to remain a fixed number. For example, if u0 is my set of initial co…

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## [BifurcationKit MethodError](https://discourse.julialang.org/t/bifurcationkit-methoderror/84904)

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**Author:** [@Dragolonth](https://discourse.julialang.org/u/Dragolonth)\
**Replies:** 3\
**Last updated:** [August 1, 2022, 6:14am UTC](https://discourse.julialang.org/t/bifurcationkit-methoderror/84904 "2022-08-01T06:14:37Z")

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Hi all. Currently, I have a reaction network defined in Catalyst, and I’ve been following the tutorial at Bifurcation Diagrams · Catalyst.jl. However, I’ve been running into an error and am not entirely sure how to resol…

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## [Mixed-Integer Multi-objective Constrained Optimization Problem Solving](https://discourse.julialang.org/t/mixed-integer-multi-objective-constrained-optimization-problem-solving/83030)

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**Author:** [@Magy](https://discourse.julialang.org/u/Magy)\
**Replies:** 4\
**Last updated:** [July 31, 2022, 11:43pm UTC](https://discourse.julialang.org/t/mixed-integer-multi-objective-constrained-optimization-problem-solving/83030 "2022-07-31T23:43:51Z")

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Dear All, I wonder if there is a direct package that can be used to solve a mixed-integer multi-objective constrained problem. I tried to use “Metaheuristics.jl” but failed to represent my model’s mixed-integer variable…

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## [Allowing Agents.jl OpenStreetMapSpace to read GeoJSON](https://discourse.julialang.org/t/allowing-agents-jl-openstreetmapspace-to-read-geojson/85055)

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**Author:** [@imantha](https://discourse.julialang.org/u/imantha)\
**Replies:** 1\
**Last updated:** [July 31, 2022, 7:15pm UTC](https://discourse.julialang.org/t/allowing-agents-jl-openstreetmapspace-to-read-geojson/85055 "2022-07-31T19:15:40Z")

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Hi I was wondering whether it would be too difficult add GeoJSON reading capabilities to agents.jl’s OpenStreetMapSpace. I am asking this as open source tools such as QGIS allows easy conversion between shp and GeoJSON …

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## [Solve many first-order ODEs](https://discourse.julialang.org/t/solve-many-first-order-odes/85060)

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**Author:** [@qwerty](https://discourse.julialang.org/u/qwerty)\
**Replies:** 6\
**Last updated:** [July 31, 2022, 6:25pm UTC](https://discourse.julialang.org/t/solve-many-first-order-odes/85060 "2022-07-31T18:25:21Z")

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What is the best way to solve so many decoupled ODEs? Possibly in parallel. Should I use Modeling Toolkit or DifferentialEquations? The equations are of the type: u’ = -a^2k^2u where a is the same for all, then I have…

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## [Any conjugate gradient method allowing a custom inner product?](https://discourse.julialang.org/t/any-conjugate-gradient-method-allowing-a-custom-inner-product/84982)

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**Author:** [@ranocha](https://discourse.julialang.org/u/ranocha)\
**Replies:** 5\
**Last updated:** [July 30, 2022, 5:57am UTC](https://discourse.julialang.org/t/any-conjugate-gradient-method-allowing-a-custom-inner-product/84982 "2022-07-30T05:57:01Z")

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Is there any conjugate gradient (CG) implementation in Julia allowing one to specify the inner product (with a fixed symmetric and positive definite matrix M, say)? In my use case, I know my system matrix A is symmetric…

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## [Control of Time-Step size in OrdinaryDiffEq](https://discourse.julialang.org/t/control-of-time-step-size-in-ordinarydiffeq/84949)

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**Author:** [@Whyborn](https://discourse.julialang.org/u/Whyborn)\
**Replies:** 4\
**Last updated:** [July 29, 2022, 11:39pm UTC](https://discourse.julialang.org/t/control-of-time-step-size-in-ordinarydiffeq/84949 "2022-07-29T23:39:52Z")

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Hi, I am trying to use OrdinaryDiffEq for the time integration of a hyperbolic PDE system in a finite-volume context. I want to control the size of the time-step through a CFL condition, rather than by some error norm. …

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## [Nonlinear curve fitting in Julia](https://discourse.julialang.org/t/nonlinear-curve-fitting-in-julia/84999)

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**Author:** [@Jian\_ZUO](https://discourse.julialang.org/u/Jian_ZUO)\
**Replies:** 4\
**Last updated:** [July 29, 2022, 9:20pm UTC](https://discourse.julialang.org/t/nonlinear-curve-fitting-in-julia/84999 "2022-07-29T21:20:33Z")

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Hi all, My question is to do a nonlinear curve fitting task (bounded) for estimating 10 parameters from several give data points, presented as follows: using Optim # my data points I = \[100.254, 94.261, 88.224, 82.193,…

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## [JuMP 2-d array Decision Variable computationally expensive](https://discourse.julialang.org/t/jump-2-d-array-decision-variable-computationally-expensive/84987)

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**Author:** [@sophiepavia](https://discourse.julialang.org/u/sophiepavia)\
**Replies:** 1\
**Last updated:** [July 29, 2022, 6:37pm UTC](https://discourse.julialang.org/t/jump-2-d-array-decision-variable-computationally-expensive/84987 "2022-07-29T18:37:00Z")

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I am creating a decision variable that is a 2-d array of size 25122 x 25122. (length of arcs and od are both 25122) Is there a more efficient way to initialize a multi-dimensional array as a decision variable? I have ch…

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