# Numerics

**URL:** https://discourse.julialang.org/c/domain/numerics/20.md?page=28

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**Page:** 29

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## [DifferentialEquations: ┌ Warning: IDAGetDky failed with error code](https://discourse.julialang.org/t/differentialequations-warning-idagetdky-failed-with-error-code/52195)

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**Author:** [@JuhaHeiskala](https://discourse.julialang.org/u/JuhaHeiskala)\
**Replies:** 10\
**Last updated:** [December 22, 2020, 11:30pm UTC](https://discourse.julialang.org/t/differentialequations-warning-idagetdky-failed-with-error-code/52195 "2020-12-22T23:30:40Z")

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I tried a test case from Octave ode15i tests and get the error: \[IDAS ERROR\] IDAGetDky Illegal value for k. ┌ Warning: IDAGetDky failed with error code = │ flag = -25 └ @ Sundials ~/.julia/dev/Sundials/src/simpl…

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## [Method Error: No mathching method when using ContinuousDynamicalSystem](https://discourse.julialang.org/t/method-error-no-mathching-method-when-using-continuousdynamicalsystem/52040)

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**Author:** [@Gary\_McCormack](https://discourse.julialang.org/u/Gary_McCormack)\
**Replies:** 7\
**Last updated:** [December 19, 2020, 4:31pm UTC](https://discourse.julialang.org/t/method-error-no-mathching-method-when-using-continuousdynamicalsystem/52040 "2020-12-19T16:31:56Z")

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Hi everyone, I’m very new to Julia and trying to wrap my head around the following error. This is a stripped-down version of the ODE I am trying to wrap as a Continuous Dynamical System. using DifferentialEquations usi…

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## [KernelDensity.jl vs scipy.stats' gaussian\_kde](https://discourse.julialang.org/t/kerneldensity-jl-vs-scipy-stats-gaussian-kde/51917)

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**Author:** [@danielalfonsetti](https://discourse.julialang.org/u/danielalfonsetti)\
**Replies:** 2\
**Last updated:** [December 16, 2020, 2:15pm UTC](https://discourse.julialang.org/t/kerneldensity-jl-vs-scipy-stats-gaussian-kde/51917 "2020-12-16T14:15:31Z")

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I’m trying to convert some python code to julia code, but there appears to be a discrepancy between the python KDE and the julia KDE. Here is a reproducible example, similar to what is happening in my project: Python: f…

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## [How to add, subtract, and take linear combinations of ODE solutions](https://discourse.julialang.org/t/how-to-add-subtract-and-take-linear-combinations-of-ode-solutions/51791)

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**Author:** [@CosmoProf](https://discourse.julialang.org/u/CosmoProf)\
**Replies:** 2\
**Last updated:** [December 15, 2020, 10:24am UTC](https://discourse.julialang.org/t/how-to-add-subtract-and-take-linear-combinations-of-ode-solutions/51791 "2020-12-15T10:24:55Z")

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Hi, I’m solving differential equations with different sets of initial conditions, and I’m trying to figure out how to take different linear combinations of the ODE solutions (added, subtracted, multiplied by different sc…

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## [DoubleFloats.jl -\> Double128 | Quad64?](https://discourse.julialang.org/t/doublefloats-jl-double128-quad64/51049)

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**Author:** [@lrnv](https://discourse.julialang.org/u/lrnv)\
**Replies:** 54\
**Last updated:** [December 14, 2020, 11:10pm UTC](https://discourse.julialang.org/t/doublefloats-jl-double128-quad64/51049 "2020-12-14T23:10:39Z")

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Hey, I need some kind of high precision arithmetics to do computations, and I’m trying to find the best balance between runtime and precision. Using BigFloat, i found out that 256bits BigFloats give me good enough resul…

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## [Julia DifferentialEquations: modify multiple states of the integrator at once](https://discourse.julialang.org/t/julia-differentialequations-modify-multiple-states-of-the-integrator-at-once/51705)

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**Author:** [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Replies:** 2\
**Last updated:** [December 12, 2020, 1:37pm UTC](https://discourse.julialang.org/t/julia-differentialequations-modify-multiple-states-of-the-integrator-at-once/51705 "2020-12-12T13:37:52Z")

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Hello, I have this model of interactions between bacteria and phages: using DifferentialEquations function payneJansenODE!(du, u, p, t) μ , φ, η, β, ω = p H = h = 0 #= du\[1\] = susceptible du\[2\] …

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## [How to force variable to zero upon meeting condition in Julia DifferentialEquations](https://discourse.julialang.org/t/how-to-force-variable-to-zero-upon-meeting-condition-in-julia-differentialequations/51655)

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**Author:** [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Replies:** 19\
**Last updated:** [December 11, 2020, 5:54pm UTC](https://discourse.julialang.org/t/how-to-force-variable-to-zero-upon-meeting-condition-in-julia-differentialequations/51655 "2020-12-11T17:54:52Z")

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Hello, I have this model of bacteria and phage interactions: using DifferentialEquations function payneJansenODE!(du, u, p, t) μ , φ, η, β, ω = p H = h = 0 du\[1\] = (μ \* u\[1\]) - (φ \* u\[1\] \* u\[3\]) - (H \* u\[1\]…

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## [Julia's FEM Landscape: where should DifferentialEquations go?](https://discourse.julialang.org/t/julias-fem-landscape-where-should-differentialequations-go/1592)

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**Author:** [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Replies:** 37\
**Last updated:** [December 10, 2020, 10:05pm UTC](https://discourse.julialang.org/t/julias-fem-landscape-where-should-differentialequations-go/1592 "2020-12-10T22:05:49Z")

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Hey, I am taking a good hard look at the Julia FEM landscape and would like some input. Let me first explain what I see the domain and scope of DifferentialEquations.jl. My work and research is centered around solving di…

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## [How to modulate the resolution of Julia DifferentialEquations solver](https://discourse.julialang.org/t/how-to-modulate-the-resolution-of-julia-differentialequations-solver/51561)

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**Author:** [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Replies:** 6\
**Last updated:** [December 10, 2020, 8:00pm UTC](https://discourse.julialang.org/t/how-to-modulate-the-resolution-of-julia-differentialequations-solver/51561 "2020-12-10T20:00:21Z")

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Hello, I have this model with delayed differential equations: using DifferentialEquations # function function baseInfect!(du, u, p, t) μ, κ, φ, ω, η, β = p du\[1\] = ((μ \* u\[1\]) \* (1 - ((u\[1\]+u\[2\])/κ))) - (φ \* u\[…

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## [Interpolation on non-rectangular domain](https://discourse.julialang.org/t/interpolation-on-non-rectangular-domain/51568)

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**Author:** [@Honza9723](https://discourse.julialang.org/u/Honza9723)\
**Replies:** 12\
**Last updated:** [December 10, 2020, 6:12pm UTC](https://discourse.julialang.org/t/interpolation-on-non-rectangular-domain/51568 "2020-12-10T18:12:08Z")

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Dear all, I would like to ask for advice, how to interpolate function on a non-rectangular domain. I am working on a problem, where the domain of my function is 2 or 3 dimensional, where all variables are restricted to …

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## [DifferentialEquations.jl: Complex function results in Inexact Error](https://discourse.julialang.org/t/differentialequations-jl-complex-function-results-in-inexact-error/51591)

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**Author:** [@ess3sq](https://discourse.julialang.org/u/ess3sq)\
**Replies:** 5\
**Last updated:** [December 10, 2020, 12:57pm UTC](https://discourse.julialang.org/t/differentialequations-jl-complex-function-results-in-inexact-error/51591 "2020-12-10T12:57:50Z")

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I am trying to solve a one dimensional Schrödinger equation which has been reduced to a first-order linear ODE of the kind \\psi’(x) = f(x) \\psi(x), where all functions have complex args (Complex{Float64}) I believe. Eit…

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## [How to debug ODE](https://discourse.julialang.org/t/how-to-debug-ode/50576)

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**Author:** [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Replies:** 14\
**Last updated:** [December 10, 2020, 6:59am UTC](https://discourse.julialang.org/t/how-to-debug-ode/50576 "2020-12-10T06:59:22Z")

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Hello, I have a set of ODEs to model a bacterial infection: function kinInfect!(du, u, p, t) μ , φ, η, β, ω, χ, ε = p H = h = 0 #= du\[1\] = susceptible du\[2\] = infected du\[3\] = phages μ…

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## [Package to solve the Maxey-Riley equation with Basset history term](https://discourse.julialang.org/t/package-to-solve-the-maxey-riley-equation-with-basset-history-term/51079)

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**Author:** [@mleprovost](https://discourse.julialang.org/u/mleprovost)\
**Replies:** 0\
**Last updated:** [December 2, 2020, 2:44am UTC](https://discourse.julialang.org/t/package-to-solve-the-maxey-riley-equation-with-basset-history-term/51079 "2020-12-02T02:44:18Z")

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Hello, Is there a Julia package to solve the Maxey-Riley equation (equation (1) of this paper https://arxiv.org/pdf/1310.2450.pdf), that governs the motion of a small sphere immersed in a fluid. This equation is a secon…

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## [How to find inflection point of curve?](https://discourse.julialang.org/t/how-to-find-inflection-point-of-curve/50892)

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**Author:** [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Replies:** 20\
**Last updated:** [November 30, 2020, 7:56am UTC](https://discourse.julialang.org/t/how-to-find-inflection-point-of-curve/50892 "2020-11-30T07:56:38Z")

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Hello, I have the function y = ϑ - ((1/ω) \* log(x/ε)) - 1/μ Is there a simple way in Julia to find the flection point of the function? if I set these paramaters: mu = 0.72 # maximum growth rate resistant (…

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## [Solving ODE based on experimental data (DifferentialEquations.jl)](https://discourse.julialang.org/t/solving-ode-based-on-experimental-data-differentialequations-jl/51002)

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**Author:** [@maajdl](https://discourse.julialang.org/u/maajdl)\
**Replies:** 4\
**Last updated:** [November 30, 2020, 9:09pm UTC](https://discourse.julialang.org/t/solving-ode-based-on-experimental-data-differentialequations-jl/51002 "2020-11-30T21:09:51Z")

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Hello, I am solving a simple ODE system with 5 state variables. It is essentially made of 5 coupled RC sytems with a few (current) excitations. These excitations are 6000 experimental data measured every 10 minutes. …

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## [How to get components of vector solution in Gridap](https://discourse.julialang.org/t/how-to-get-components-of-vector-solution-in-gridap/50882)

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**Author:** [@jmura](https://discourse.julialang.org/u/jmura)\
**Replies:** 0\
**Last updated:** [November 27, 2020, 11:43pm UTC](https://discourse.julialang.org/t/how-to-get-components-of-vector-solution-in-gridap/50882 "2020-11-27T23:43:25Z")

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Dear Julia users, I’m using Gridap, and I’m learning from the tutorials. I have some questions: a) How can we recover x- or y-components from a numerical solution uh, as the solution to linear elasticity (like in the t…

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## [Package/algorithm for barycentric grid interpolation](https://discourse.julialang.org/t/package-algorithm-for-barycentric-grid-interpolation/50803)

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**Author:** [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Replies:** 6\
**Last updated:** [November 27, 2020, 3:16pm UTC](https://discourse.julialang.org/t/package-algorithm-for-barycentric-grid-interpolation/50803 "2020-11-27T15:16:35Z")

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I am looking for a package or an algorithm (which I am happy to code into a package and make it available) that expresses a coordinate inside a simplex as a convex combination “near” of points with integer coordinates. F…

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## [IterativeSolvers and Positive Definite Matrices](https://discourse.julialang.org/t/iterativesolvers-and-positive-definite-matrices/50292)

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**Author:** [@Jonas](https://discourse.julialang.org/u/Jonas)\
**Replies:** 18\
**Last updated:** [November 27, 2020, 9:36am UTC](https://discourse.julialang.org/t/iterativesolvers-and-positive-definite-matrices/50292 "2020-11-27T09:36:24Z")

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Hello dear Julia Users, In order to calculate eigenvalues and vectors I am currently using the package IterativeSolvers, but I often get the error that my input matrices are not positive definite. My code is like this: …

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## [Approximating A+B\*log with NeuralNetwork](https://discourse.julialang.org/t/approximating-a-b-log-with-neuralnetwork/50709)

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**Author:** [@Honza9723](https://discourse.julialang.org/u/Honza9723)\
**Replies:** 0\
**Last updated:** [November 24, 2020, 7:57pm UTC](https://discourse.julialang.org/t/approximating-a-b-log-with-neuralnetwork/50709 "2020-11-24T19:57:22Z")

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Dear All, I am working on an economics project which utilizes neural networks as a method for approximation of model solutions (those models are systems of differential/difference equations). For some versions of these …

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## [Arbitrary precision computations: BigFloat and ArbNumerics.jl](https://discourse.julialang.org/t/arbitrary-precision-computations-bigfloat-and-arbnumerics-jl/50645)

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**Author:** [@lrnv](https://discourse.julialang.org/u/lrnv)\
**Replies:** 8\
**Last updated:** [November 24, 2020, 9:41am UTC](https://discourse.julialang.org/t/arbitrary-precision-computations-bigfloat-and-arbnumerics-jl/50645 "2020-11-24T09:41:35Z")

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Hey, I have troubles to understand why arbitrary precision in Julia has to go through C code, like biglofats (that uses the mpfr library), and ArbNumerics (that uses the Arb library). Although these are stunning packag…

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## [Julia DifferentialEquations: add two delays into ODE](https://discourse.julialang.org/t/julia-differentialequations-add-two-delays-into-ode/50362)

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**Author:** [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Replies:** 14\
**Last updated:** [November 22, 2020, 8:13am UTC](https://discourse.julialang.org/t/julia-differentialequations-add-two-delays-into-ode/50362 "2020-11-22T08:13:14Z")

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Hello, I have a set of ODEs to model the invasion of a bacterium in presence of phages. I have inserted the invading bacterium at t=1000 using a delay. function multiInfect!(du, u, p, t) μ, ν, κ, φ, ψ, ω, β, Β, ρ, …

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## [Generate singular value sequentialy](https://discourse.julialang.org/t/generate-singular-value-sequentialy/50434)

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**Author:** [@Geoffrey](https://discourse.julialang.org/u/Geoffrey)\
**Replies:** 2\
**Last updated:** [November 19, 2020, 2:13pm UTC](https://discourse.julialang.org/t/generate-singular-value-sequentialy/50434 "2020-11-19T14:13:25Z")

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Hi, I’m wondering if there is a way of generating singular value sequentialy. I’m aware of the truncated svd utilities from TSVD.jl and LowRankApprox.jl but to my knowledge they didn’t provide a way to generate singular…

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## [How do I do a plain old "A=LU" decomposition of sparse matrices?](https://discourse.julialang.org/t/how-do-i-do-a-plain-old-a-lu-decomposition-of-sparse-matrices/49619)

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**Author:** [@casey\_watkins](https://discourse.julialang.org/u/casey_watkins)\
**Replies:** 7\
**Last updated:** [November 19, 2020, 1:16am UTC](https://discourse.julialang.org/t/how-do-i-do-a-plain-old-a-lu-decomposition-of-sparse-matrices/49619 "2020-11-19T01:16:29Z")

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I have a very large sparse matrix A and need to produce L, U such that A=L\*U for the specific type of problem I am solving. I am aware of LinearAlgebra.lu, where setting the “pivot” flag to false accomplishes this. This…

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## [Query status of the solution when using Roots](https://discourse.julialang.org/t/query-status-of-the-solution-when-using-roots/50328)

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**Author:** [@optimist](https://discourse.julialang.org/u/optimist)\
**Replies:** 4\
**Last updated:** [November 18, 2020, 7:08pm UTC](https://discourse.julialang.org/t/query-status-of-the-solution-when-using-roots/50328 "2020-11-18T19:08:51Z")

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Edited to make it more specific I would like to query status of the solution when using the Roots package, before the function returns an answer. I can see in the source code of “find\_zero.jl” that it has some functiona…

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## [Arpack and MKL](https://discourse.julialang.org/t/arpack-and-mkl/50291)

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**Author:** [@Jonas](https://discourse.julialang.org/u/Jonas)\
**Replies:** 1\
**Last updated:** [November 18, 2020, 9:07am UTC](https://discourse.julialang.org/t/arpack-and-mkl/50291 "2020-11-18T09:07:20Z")

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Hello everyone, I wrote some code to calculate the first n eigenvalues and eigenvectors of a generalized eigenvalue problem over a two-dimensional mesh. For this I used the function eigs() of the package Arpack. Since t…

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## [Julia DifferentialEquations: increase maxiter](https://discourse.julialang.org/t/julia-differentialequations-increase-maxiter/50318)

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**Author:** [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Replies:** 6\
**Last updated:** [November 18, 2020, 7:57am UTC](https://discourse.julialang.org/t/julia-differentialequations-increase-maxiter/50318 "2020-11-18T07:57:54Z")

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Hello, I have set an ODEProblem object, but the procedure is stopped (although I still get t a solution) because a higher maxiters is needed. How can I check what is the default value and what is the syntax to increase…

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## [Julia DifferentialEquations: add delay into ODE](https://discourse.julialang.org/t/julia-differentialequations-add-delay-into-ode/50337)

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**Author:** [@Luigi\_Marongiu](https://discourse.julialang.org/u/Luigi_Marongiu)\
**Replies:** 3\
**Last updated:** [November 18, 2020, 7:03am UTC](https://discourse.julialang.org/t/julia-differentialequations-add-delay-into-ode/50337 "2020-11-18T07:03:01Z")

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Hello, I have a set of ODE to model the growth of bacteria nad phages: function multiInfect!(du, u, p, t) μ, ν, κ, φ, ψ, ω, β, Β, ρ, τ, η, Η = p #= du\[1\] = resident susceptible du\[2\] = resident infected…

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## [In-place orthogonal/unitary transforms?](https://discourse.julialang.org/t/in-place-orthogonal-unitary-transforms/50111)

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**Author:** [@pkairys](https://discourse.julialang.org/u/pkairys)\
**Replies:** 12\
**Last updated:** [November 17, 2020, 10:46am UTC](https://discourse.julialang.org/t/in-place-orthogonal-unitary-transforms/50111 "2020-11-17T10:46:43Z")

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Say I want to perform a unitary/orthogonal transformation of an operator: U^\\dagger A U Is there a way to do this without allocating a new array? I see that there is a method for lmul!(A,B) that will do AB and place t…

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## [Krylov subspace polynomial of one right hand side, applied to another](https://discourse.julialang.org/t/krylov-subspace-polynomial-of-one-right-hand-side-applied-to-another/50250)

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**Author:** [@raminammour](https://discourse.julialang.org/u/raminammour)\
**Replies:** 0\
**Last updated:** [November 16, 2020, 9:24pm UTC](https://discourse.julialang.org/t/krylov-subspace-polynomial-of-one-right-hand-side-applied-to-another/50250 "2020-11-16T21:24:17Z")

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Hello, A Krylov subspace method (gmres, cg, minres,…) approximates the solution of a linear system, Ax=b. The solution at iteration n is a polynomial in A, applied to the right hand side b: x\_n = P\_n(A,b) b. Note that P…

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## [How do I use eigen! with my input matrix?](https://discourse.julialang.org/t/how-do-i-use-eigen-with-my-input-matrix/49997)

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**Author:** [@Noel\_Araujo](https://discourse.julialang.org/u/Noel_Araujo)\
**Replies:** 4\
**Last updated:** [November 11, 2020, 7:42pm UTC](https://discourse.julialang.org/t/how-do-i-use-eigen-with-my-input-matrix/49997 "2020-11-11T19:42:35Z")

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Hello I have an idea, but i don’t know how to implemented it. I would like to pass a temporary variables to store the eigenvectors of eigen! - by default eigen! uses the original matrix. I am confident that this is pos…

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