# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?page=528

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**Page:** 529

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## [How to (row) append two JuliaDB tables together?](https://discourse.julialang.org/t/how-to-row-append-two-juliadb-tables-together/14228)

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**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 1\
**Last updated:** [August 29, 2018, 9:11am UTC](https://discourse.julialang.org/t/how-to-row-append-two-juliadb-tables-together/14228 "2018-08-29T09:11:45Z")

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How do I (row) append two JuliaDB tables togehter? In DataFrames.jl \[data1;data2\] is sufficient, but the same syntax doesn’t work in JuliaDB. Also How do I append table 2 to table 1 by modifying table 1? See MWE using…

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## [Compose.jl basic usage](https://discourse.julialang.org/t/compose-jl-basic-usage/14185)

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**Author:** [@LaurentPlagne](https://discourse.julialang.org/u/LaurentPlagne)\
**Replies:** 4\
**Last updated:** [August 29, 2018, 7:03am UTC](https://discourse.julialang.org/t/compose-jl-basic-usage/14185 "2018-08-29T07:03:06Z")

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Hi, I try to use compose.jl and I fail to understand the very basic usage of it. I want to draw a circle and a text, and it works until I try to put a black line around the circle (stroke which is not in the documentat…

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## [Right multiplication of Diagonal matrix](https://discourse.julialang.org/t/right-multiplication-of-diagonal-matrix/12590)

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**Author:** [@pochoi](https://discourse.julialang.org/u/pochoi)\
**Replies:** 2\
**Last updated:** [August 29, 2018, 2:28am UTC](https://discourse.julialang.org/t/right-multiplication-of-diagonal-matrix/12590 "2018-08-29T02:28:56Z")

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In Julia 0.7 using SparseArrays n = 1000 @time Diagonal(1:n) \* sparse(1:n, n:-1:1, 1:n) @time sparse(1:n, n:-1:1, 1:n) \* Diagonal(1:n) 0.002262 seconds (42 allocations: 110.125 KiB) 0.893608 seconds (39 allocations:…

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## [How does cache works in JuliaDiffEq?](https://discourse.julialang.org/t/how-does-cache-works-in-juliadiffeq/14214)

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**Author:** [@wsrinin](https://discourse.julialang.org/u/wsrinin)\
**Replies:** 1\
**Last updated:** [August 29, 2018, 12:15am UTC](https://discourse.julialang.org/t/how-does-cache-works-in-juliadiffeq/14214 "2018-08-29T00:15:28Z")

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Hi, I am trying to understand the internal of JuliaDiffEq package. I have encountered many files names sth\_cache.jl. Can anyone explain to me what do these files do and why we need it? I tried to find the explanations i…

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## [CSV Reader / Writer Choices](https://discourse.julialang.org/t/csv-reader-writer-choices/14218)

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**Author:** [@iwelch](https://discourse.julialang.org/u/iwelch)\
**Replies:** 1\
**Last updated:** [August 28, 2018, 11:16pm UTC](https://discourse.julialang.org/t/csv-reader-writer-choices/14218 "2018-08-28T23:16:35Z")

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Has someone compared the various packages to read and write csv files (e.g., readtables, DelimitedFiles and CSV)?

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## [Repeated Solving of Linear System with the Same Structure](https://discourse.julialang.org/t/repeated-solving-of-linear-system-with-the-same-structure/14153)

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**Author:** [@Juser](https://discourse.julialang.org/u/Juser)\
**Replies:** 7\
**Last updated:** [August 28, 2018, 10:57pm UTC](https://discourse.julialang.org/t/repeated-solving-of-linear-system-with-the-same-structure/14153 "2018-08-28T22:57:34Z")

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UPDATE WITH MORE COMPLETE EXAMPLE The advice already provided has been extremely helpful, and I am adding this update to provide greater detail and a more concrete example in case it spurs any other thoughts/advice. The…

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## [Optim.jl - computing value, gradient and hessian simultaneously](https://discourse.julialang.org/t/optim-jl-computing-value-gradient-and-hessian-simultaneously/1219)

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**Author:** [@piever](https://discourse.julialang.org/u/piever)\
**Replies:** 17\
**Last updated:** [August 28, 2018, 7:58pm UTC](https://discourse.julialang.org/t/optim-jl-computing-value-gradient-and-hessian-simultaneously/1219 "2018-08-28T19:58:45Z")

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I’ve seen in the documentation of Optim.jl that there is a basic trick to avoid recomputing the same quantity when evaluating a function and its gradient (and potentially also its hessian). The idea is to store whatever …

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## [Need help with NLopt AUGLAG termination criteria](https://discourse.julialang.org/t/need-help-with-nlopt-auglag-termination-criteria/14189)

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**Author:** [@ivborissov](https://discourse.julialang.org/u/ivborissov)\
**Replies:** 0\
**Last updated:** [August 28, 2018, 12:57pm UTC](https://discourse.julialang.org/t/need-help-with-nlopt-auglag-termination-criteria/14189 "2018-08-28T12:57:49Z")

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Hi, I have an optimization problem with equality constraints and I use NLopt LN\_AUGLAG solver with derivative-free local solver like LN\_NELDERMEAD or LN\_SBPLX. However I don’t have a clear understanding how to choose to…

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## [Error with Julia 1.0 + Plots with GR and PyPlot + Conda](https://discourse.julialang.org/t/error-with-julia-1-0-plots-with-gr-and-pyplot-conda/14118)

<div class="topic-metadata">

**Author:** [@v-i-s-h](https://discourse.julialang.org/u/v-i-s-h)\
**Replies:** 6\
**Last updated:** [August 28, 2018, 6:34am UTC](https://discourse.julialang.org/t/error-with-julia-1-0-plots-with-gr-and-pyplot-conda/14118 "2018-08-28T06:34:34Z")

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Hi, I’m using Julia 1.0 and is trying to use Plots for my plotting. For PyCall, I’m using system conda installation. julia\> versioninfo() Julia Version 1.0.0 Commit 5d4eaca0c9 (2018-08-08 20:58 UTC) Platform Info: OS…

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## [The equivalent of R's var() for matrix?](https://discourse.julialang.org/t/the-equivalent-of-rs-var-for-matrix/14148)

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**Author:** [@DominiqueMakowski](https://discourse.julialang.org/u/DominiqueMakowski)\
**Replies:** 2\
**Last updated:** [August 27, 2018, 6:35pm UTC](https://discourse.julialang.org/t/the-equivalent-of-rs-var-for-matrix/14148 "2018-08-27T18:35:10Z")

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I am trying to reproduce the following R code in Julia: simdata\_correlation \<- function(coefs=c(0.2, 0.5), n=100){ # Generate outcome y \<- rnorm(n, 0, 1) n\_var \<- length(coefs) X \<- scale(matrix(rnorm(n\*(n\_var…

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## [Supported Attributes tables in Plots documentaion disappeared](https://discourse.julialang.org/t/supported-attributes-tables-in-plots-documentaion-disappeared/14069)

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**Author:** [@Carsten](https://discourse.julialang.org/u/Carsten)\
**Replies:** 2\
**Last updated:** [August 27, 2018, 10:56am UTC](https://discourse.julialang.org/t/supported-attributes-tables-in-plots-documentaion-disappeared/14069 "2018-08-27T10:56:40Z")

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In Plots documentation no Supported Attributes are enlisted anymore. Instead I’ve got: # 404 \*\*File not found\*\* The site configured at this address does not contain the requested file.

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## [JuMP solver callback arguments](https://discourse.julialang.org/t/jump-solver-callback-arguments/13936)

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**Author:** [@Zacharie\_ALES](https://discourse.julialang.org/u/Zacharie_ALES)\
**Replies:** 4\
**Last updated:** [August 27, 2018, 9:02am UTC](https://discourse.julialang.org/t/jump-solver-callback-arguments/13936 "2018-08-27T09:02:06Z")

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Hello, I use CPLEX and a callback to solve several instances of a problem. In the callback I need to access variables (for example it could be the size of the problem or any additional information about the instance cu…

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## [Venn Diagram](https://discourse.julialang.org/t/venn-diagram/14084)

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**Author:** [@sampie](https://discourse.julialang.org/u/sampie)\
**Replies:** 2\
**Last updated:** [August 27, 2018, 6:37am UTC](https://discourse.julialang.org/t/venn-diagram/14084 "2018-08-27T06:37:30Z")

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Hi, I am wondering how to draw a venn diagram with language. What is a preferred and well supported way of doing that in Julia language? I would be happy if there was some example code that would work out of the box. I …

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## [The kernel appears to have died. It will restart automatically, when using NLopt](https://discourse.julialang.org/t/the-kernel-appears-to-have-died-it-will-restart-automatically-when-using-nlopt/11362)

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**Author:** [@Ludo](https://discourse.julialang.org/u/Ludo)\
**Replies:** 1\
**Last updated:** [August 26, 2018, 2:06pm UTC](https://discourse.julialang.org/t/the-kernel-appears-to-have-died-it-will-restart-automatically-when-using-nlopt/11362 "2018-08-26T14:06:14Z")

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Trying to find a solve a NL system using a derivative-free (LN\_COBYLA or GN\_ISRES) algorithm with NLopt, within JuMP. I receive the following error message: The kernel appears to have died. It will restart automatically…

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## [Transparency in surface plots](https://discourse.julialang.org/t/transparency-in-surface-plots/14099)

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**Author:** [@Alvaro\_Jose\_Gonzalez](https://discourse.julialang.org/u/Alvaro_Jose_Gonzalez)\
**Replies:** 1\
**Last updated:** [August 26, 2018, 11:05pm UTC](https://discourse.julialang.org/t/transparency-in-surface-plots/14099 "2018-08-26T23:05:13Z")

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I am making a surface under Plots.jl (pyplot backend) and cannot change the transparency of the surface. I have played with the parameter alpha, but no results. Any tips?

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## [JuMP Ipopt on Julia 0.7](https://discourse.julialang.org/t/jump-ipopt-on-julia-0-7/14041)

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**Author:** [@Bernard\_GODARD](https://discourse.julialang.org/u/Bernard_GODARD)\
**Replies:** 4\
**Last updated:** [August 26, 2018, 3:35pm UTC](https://discourse.julialang.org/t/jump-ipopt-on-julia-0-7/14041 "2018-08-26T15:35:32Z")

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This is a continuation of Julia 0.7 and JuMP: ERROR: cosd is not defined for type Variable - #5 by tkoolen trying to get my JuMP problem converted to Julia 0.7. How to create an Ipopt problem with JuMP on Julia 0.7? Acc…

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## [Julia 1.0 Example of @distributed and pmap](https://discourse.julialang.org/t/julia-1-0-example-of-distributed-and-pmap/14064)

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**Author:** [@iwelch](https://discourse.julialang.org/u/iwelch)\
**Replies:** 1\
**Last updated:** [August 26, 2018, 2:56am UTC](https://discourse.julialang.org/t/julia-1-0-example-of-distributed-and-pmap/14064 "2018-08-26T02:56:14Z")

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I am unable to get @distributed (aka @parallel) to work, even with a trivial example. I get errors. is it obvious what I am doing wrong? $ julia \_ \_ \_ \_(\_)\_ | Documentation: https://docs.…

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## [JuMP beginners help](https://discourse.julialang.org/t/jump-beginners-help/14016)

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**Author:** [@Jon\_Norberg](https://discourse.julialang.org/u/Jon_Norberg)\
**Replies:** 2\
**Last updated:** [August 25, 2018, 6:18am UTC](https://discourse.julialang.org/t/jump-beginners-help/14016 "2018-08-25T06:18:22Z")

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Hi, I have the following problem: N=10 r=rand(N)\*2 a=rand(N,N)\*0.5-0.25 \[a\[i,i\]=1.0 for i=1:N\] m = Model(solver = NLoptSolver(algorithm=:LD\_MMA)) @variable(m, x\[1:N\] \>= 0 ) @variable(m, 1.0 \>= h\[1:N…

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## [Heuristic methods for solving the p-median problem](https://discourse.julialang.org/t/heuristic-methods-for-solving-the-p-median-problem/14022)

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**Author:** [@Stuart\_Rogers](https://discourse.julialang.org/u/Stuart_Rogers)\
**Replies:** 0\
**Last updated:** [August 25, 2018, 3:00am UTC](https://discourse.julialang.org/t/heuristic-methods-for-solving-the-p-median-problem/14022 "2018-08-25T03:00:53Z")

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Are there any Julia implementations of heuristic methods (e.g. genetic algorithm, simulated annealing, tabu search, variable neighborhood search) for solving the p-median problem? I did find a Lagrangian relaxation imple…

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## [Why the reshape in Flux mnist convolution example](https://discourse.julialang.org/t/why-the-reshape-in-flux-mnist-convolution-example/13973)

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**Author:** [@hskramer](https://discourse.julialang.org/u/hskramer)\
**Replies:** 1\
**Last updated:** [August 25, 2018, 12:57am UTC](https://discourse.julialang.org/t/why-the-reshape-in-flux-mnist-convolution-example/13973 "2018-08-25T00:57:02Z")

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I have learned to use most of the ML packages and I can compute the outcome of convolutions given kernel, stride pad…, but I don’t understand why or how to do a reshape when using Flux with convolutions and probably oth…

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## [Share a modules between processes](https://discourse.julialang.org/t/share-a-modules-between-processes/13903)

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**Author:** [@vitreo12](https://discourse.julialang.org/u/vitreo12)\
**Replies:** 0\
**Last updated:** [August 22, 2018, 7:51pm UTC](https://discourse.julialang.org/t/share-a-modules-between-processes/13903 "2018-08-22T19:51:46Z")

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Duplicate of: Share a module between two Worker processes Sorry for the mistake.

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## [IJulia: Save a Image from PyPlot as PDF in JupyterLab](https://discourse.julialang.org/t/ijulia-save-a-image-from-pyplot-as-pdf-in-jupyterlab/12880)

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**Author:** [@v-i-s-h](https://discourse.julialang.org/u/v-i-s-h)\
**Replies:** 1\
**Last updated:** [August 23, 2018, 2:54pm UTC](https://discourse.julialang.org/t/ijulia-save-a-image-from-pyplot-as-pdf-in-jupyterlab/12880 "2018-08-23T14:54:29Z")

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Hi, I use jupyter-lab with IJulia kernel for my research. I use PyPlot for my plotting. When using normal Julia scripts, I’m able to use figure() # ... Code to Plot data... savefig( "my\_results.pdf", bbox\_inches = "t…

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## [\[ANN\] MixedDistributions.jl to manipulate mixed discrete-continuous variables](https://discourse.julialang.org/t/ann-mixeddistributions-jl-to-manipulate-mixed-discrete-continuous-variables/13935)

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**Author:** [@mbesancon](https://discourse.julialang.org/u/mbesancon)\
**Replies:** 0\
**Last updated:** [August 23, 2018, 12:17pm UTC](https://discourse.julialang.org/t/ann-mixeddistributions-jl-to-manipulate-mixed-discrete-continuous-variables/13935 "2018-08-23T12:17:00Z")

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Built on top of Distributions.jl, the goal of MixedDistributions is to represent and manipulate discrete-continuous variables. An informal definition of such variable is a continuous distribution with mass points (the C…

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## [Discrete variables over continuous](https://discourse.julialang.org/t/discrete-variables-over-continuous/13934)

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**Author:** [@mbesancon](https://discourse.julialang.org/u/mbesancon)\
**Replies:** 0\
**Last updated:** [August 23, 2018, 12:07pm UTC](https://discourse.julialang.org/t/discrete-variables-over-continuous/13934 "2018-08-23T12:07:23Z")

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From Distributions.jl source: https://github.com/JuliaStats/Distributions.jl/blob/9b7a3483ae5e96a77d406cdce8aa9de0180484f0/src/common.jl#L12 Can’t a discrete distribution have a support over real numbers outside of int…

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## [Finding jumps/discontinuities in a univariate function](https://discourse.julialang.org/t/finding-jumps-discontinuities-in-a-univariate-function/13919)

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**Author:** [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Replies:** 4\
**Last updated:** [August 23, 2018, 8:20am UTC](https://discourse.julialang.org/t/finding-jumps-discontinuities-in-a-univariate-function/13919 "2018-08-23T08:20:32Z")

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I want to find jumps (or at least one jump, if it exists) in a univariate function on a given interval. Eg looking for a jump in f(x) = x \> 0 ? one(x) : zero(x) on \[-2,2\] should give me \\approx 0. I searched the liter…

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## [Singular Exceptions on Windows OS](https://discourse.julialang.org/t/singular-exceptions-on-windows-os/13877)

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**Author:** [@HSFengWang](https://discourse.julialang.org/u/HSFengWang)\
**Replies:** 9\
**Last updated:** [August 23, 2018, 8:14am UTC](https://discourse.julialang.org/t/singular-exceptions-on-windows-os/13877 "2018-08-23T08:14:50Z")

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When I use LsqFit to loop some curve fitting, I come across some singular exceptions. Anyone could give me some guidance on this problem. My os is window 32. Thank you. func(x, p) = 1 ./ (p\[1\]+p\[2\] \* exp.(-p\[3\] \* x ))…

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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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## [Question About Transposes and Matrix Multiplication Speed](https://discourse.julialang.org/t/question-about-transposes-and-matrix-multiplication-speed/13870)

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**Author:** [@Juser](https://discourse.julialang.org/u/Juser)\
**Replies:** 9\
**Last updated:** [August 22, 2018, 6:00pm UTC](https://discourse.julialang.org/t/question-about-transposes-and-matrix-multiplication-speed/13870 "2018-08-22T18:00:48Z")

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I’ve noticed that for Julia 0.7.0 that A\*c is faster than A'\*c in the following case, when I would have expected that A' would make the align the memory more easily for the computer to perform the matrix multiplication. …

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## [Trying to plot freezes Julia?](https://discourse.julialang.org/t/trying-to-plot-freezes-julia/13879)

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**Author:** [@HelgavonLichtenstein](https://discourse.julialang.org/u/HelgavonLichtenstein)\
**Replies:** 17\
**Last updated:** [August 22, 2018, 2:58pm UTC](https://discourse.julialang.org/t/trying-to-plot-freezes-julia/13879 "2018-08-22T14:58:22Z")

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Hello, I am trying to create a plot using Plots.jl and have run some code but it has already been over 15 minutes with no response from Julia. The screen looks like: Is this normal? It seems unusual to me. I am using…

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