# Specific Domains

**URL:** https://discourse.julialang.org/c/domain/10.md?page=552

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**Page:** 553

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## [Stack overflow in DataFrames group by](https://discourse.julialang.org/t/stack-overflow-in-dataframes-group-by/6357)

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**Author:** [@ExpandingMan](https://discourse.julialang.org/u/ExpandingMan)\
**Replies:** 16\
**Last updated:** [October 15, 2017, 5:28pm UTC](https://discourse.julialang.org/t/stack-overflow-in-dataframes-group-by/6357 "2017-10-15T17:28:35Z")

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I have a million row data frame and I am running groupby on a column of strings: by(df, :col) do sdf DataFrame(n=size(sdf,1)) end and I get the following StackOverflowError ERROR: LoadError: StackOverflowError: St…

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## [\`Nulls.skip\` is very slow](https://discourse.julialang.org/t/nulls-skip-is-very-slow/6351)

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**Author:** [@ExpandingMan](https://discourse.julialang.org/u/ExpandingMan)\
**Replies:** 4\
**Last updated:** [October 15, 2017, 12:40pm UTC](https://discourse.julialang.org/t/nulls-skip-is-very-slow/6351 "2017-10-15T12:40:46Z")

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Please excuse how rough this example is (but I think it is essentially correct) using Nulls using BenchmarkTools const N = 10^7 const n = 10^5 A = convert(Vector{Union{Int64,Null}}, rand(Int64, N)) …

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## [Which are efficient data structures for querying data by name?](https://discourse.julialang.org/t/which-are-efficient-data-structures-for-querying-data-by-name/6285)

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**Author:** [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)\
**Replies:** 2\
**Last updated:** [October 14, 2017, 12:08pm UTC](https://discourse.julialang.org/t/which-are-efficient-data-structures-for-querying-data-by-name/6285 "2017-10-14T12:08:34Z")

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Hello, while I guess standard Array{T,n} are the most efficient data structures for positional access, I have often the need to access data by some keys. I am currently using DataFrames to access this data, using eithe…

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## [Jump heuristic isn't working (says infeasible)](https://discourse.julialang.org/t/jump-heuristic-isnt-working-says-infeasible/6428)

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**Author:** [@Wikunia](https://discourse.julialang.org/u/Wikunia)\
**Replies:** 0\
**Last updated:** [October 13, 2017, 7:33pm UTC](https://discourse.julialang.org/t/jump-heuristic-isnt-working-says-infeasible/6428 "2017-10-13T19:33:42Z")

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I have the following facility location model: m = Model(solver=GLPKSolverMIP()) @variable(m, sf\[1:N\], Bin) @variable(m, cf\[c=1:M,f=1:N\], Bin) @objective(m, Min, dot(f\_s,sf)+sum(cf\[c=j,f=i\]\*euclidean(c\_pos\[j\],f\_pos\[i\]) f…

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## [Momentum methods in Optim - do you use them?](https://discourse.julialang.org/t/momentum-methods-in-optim-do-you-use-them/6416)

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**Author:** [@pkofod](https://discourse.julialang.org/u/pkofod)\
**Replies:** 11\
**Last updated:** [October 13, 2017, 3:56pm UTC](https://discourse.julialang.org/t/momentum-methods-in-optim-do-you-use-them/6416 "2017-10-13T15:56:36Z")

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As the title suggests, I’m currently wondering if Accelerated Gradient Descent and Momentum Gradient Descent should be (re)moved from Optim. “Momentum methods” certainly have their use, and machine learning seems to hav…

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## [Problem with adding a column](https://discourse.julialang.org/t/problem-with-adding-a-column/4243)

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**Author:** [@mposs](https://discourse.julialang.org/u/mposs)\
**Replies:** 4\
**Last updated:** [October 12, 2017, 7:08pm UTC](https://discourse.julialang.org/t/problem-with-adding-a-column/4243 "2017-10-12T19:08:14Z")

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I’m trying to add an anonymous variable to two constraints but I get an error. using JuMP m = Model() @constraint(m, con1, 0 \<= 1) @constraint(m, con2, 0 \<= 1) constrrefs = Vector{ConstraintRef}(0) push!(constrrefs,con1…

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## [Integrating Leaflet into Julia](https://discourse.julialang.org/t/integrating-leaflet-into-julia/6411)

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**Author:** [@Balinus](https://discourse.julialang.org/u/Balinus)\
**Replies:** 2\
**Last updated:** [October 12, 2017, 6:28pm UTC](https://discourse.julialang.org/t/integrating-leaflet-into-julia/6411 "2017-10-12T18:28:02Z")

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Hello! I’m currently testing leaflet.js through the Python Folium package through Julia (that’s a lot of “through”). I find that the maps are really nice and I’m looking to use that framework into my package (ClimateToo…

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## [Enumerate(dict) behavior](https://discourse.julialang.org/t/enumerate-dict-behavior/5312)

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**Author:** [@sambitdash](https://discourse.julialang.org/u/sambitdash)\
**Replies:** 10\
**Last updated:** [October 11, 2017, 3:12am UTC](https://discourse.julialang.org/t/enumerate-dict-behavior/5312 "2017-10-11T03:12:00Z")

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Hi All, enumerate(iter) behavior enumerates over an index and dataItem to the associated index. For associative containers like Dict one would believe the natural iteration will be over named indexes which is the (key, …

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## [\`InexactError\` when plotting \`DateTime\` in Plots.jl](https://discourse.julialang.org/t/inexacterror-when-plotting-datetime-in-plots-jl/6379)

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**Author:** [@ExpandingMan](https://discourse.julialang.org/u/ExpandingMan)\
**Replies:** 3\
**Last updated:** [October 10, 2017, 6:04pm UTC](https://discourse.julialang.org/t/inexacterror-when-plotting-datetime-in-plots-jl/6379 "2017-10-10T18:04:21Z")

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When attempting to plot a histogram of DateTime I get the following error ERROR: LoadError: InexactError() Stacktrace: \[1\] convert(::Type{Int64}, ::Float64) at ./float.jl:679 \[2\] UTM at ./dates/types.jl:74 \[inlined\] …

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## [Leaky relu with Flux](https://discourse.julialang.org/t/leaky-relu-with-flux/6377)

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**Author:** [@skariel](https://discourse.julialang.org/u/skariel)\
**Replies:** 1\
**Last updated:** [October 10, 2017, 1:09pm UTC](https://discourse.julialang.org/t/leaky-relu-with-flux/6377 "2017-10-10T13:09:03Z")

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Any ideas how to implement LeakyRelu, getting a no method matching error on isless. Also I had to implement my own std function: Thanks! mystd(x) = sqrt(sum((x-mean(x)).^2)/(length(x)-1)) lrelu(x) = isless(x,0.0) ? 0.…

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## [Get siginificance of main fixed category effects in mixed linear model with MixedModels.jl](https://discourse.julialang.org/t/get-siginificance-of-main-fixed-category-effects-in-mixed-linear-model-with-mixedmodels-jl/6268)

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**Author:** [@ksmet1977](https://discourse.julialang.org/u/ksmet1977)\
**Replies:** 7\
**Last updated:** [October 10, 2017, 12:31pm UTC](https://discourse.julialang.org/t/get-siginificance-of-main-fixed-category-effects-in-mixed-linear-model-with-mixedmodels-jl/6268 "2017-10-10T12:31:54Z")

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Hi group, I have a dataframe of \>10000 rows of repeated measurements on 25 subjects (OB) on 3 categorical factors (QF,B,PA) and 1 continuous (CCT) factor. The first few lines look like this: │ Row │ OB │ QF │ BG │ …

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## [Triangulated surfaces in GR: ray-tracing](https://discourse.julialang.org/t/triangulated-surfaces-in-gr-ray-tracing/6348)

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**Author:** [@sswatson](https://discourse.julialang.org/u/sswatson)\
**Replies:** 1\
**Last updated:** [October 9, 2017, 2:41pm UTC](https://discourse.julialang.org/t/triangulated-surfaces-in-gr-ray-tracing/6348 "2017-10-09T14:41:00Z")

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I’m looking to use GR along with Interact.jl for a 3D visualization in IJulia, and I noticed that GR.trisurface seems to have some difficulties with overlapping polygons (as matplotlib does). Is there currently a way to…

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## [ANN: Bloomie.jl (Bloomberg BLPAPI wrapper)](https://discourse.julialang.org/t/ann-bloomie-jl-bloomberg-blpapi-wrapper/6347)

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**Author:** [@ungil](https://discourse.julialang.org/u/ungil)\
**Replies:** 0\
**Last updated:** [October 9, 2017, 1:52pm UTC](https://discourse.julialang.org/t/ann-bloomie-jl-bloomberg-blpapi-wrapper/6347 "2017-10-09T13:52:56Z")

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https://github.com/ungil/Bloomie.jl The package has been only lightly tested, it was written mostly as an exercise to try Julia and its FFI.

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## [Read(“count\_heads.jl”, String) conversion error](https://discourse.julialang.org/t/read-count-heads-jl-string-conversion-error/6253)

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**Author:** [@EconometricsBySimula](https://discourse.julialang.org/u/EconometricsBySimula)\
**Replies:** 8\
**Last updated:** [October 9, 2017, 3:43am UTC](https://discourse.julialang.org/t/read-count-heads-jl-string-conversion-error/6253 "2017-10-09T03:43:36Z")

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I am going through Parallel Loops and Maps and I am seeming to have difficulty with even accessing the file count\_heads.jl I saved it in my working directory function count\_heads(n) c::Int = 0 for i = 1:n c += rand…

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## [Run model runs in a parallel for loop in julia](https://discourse.julialang.org/t/run-model-runs-in-a-parallel-for-loop-in-julia/6326)

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**Author:** [@Simon\_Besnard](https://discourse.julialang.org/u/Simon_Besnard)\
**Replies:** 2\
**Last updated:** [October 8, 2017, 6:56pm UTC](https://discourse.julialang.org/t/run-model-runs-in-a-parallel-for-loop-in-julia/6326 "2017-10-08T18:56:36Z")

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I am trying to parallelize the code below. The idea is to run several model runs in parallel and push their output in to a single dataframe (i.e. dout). The code I have created works with no parrallelisation so far. Howe…

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## [Exact linear algebra](https://discourse.julialang.org/t/exact-linear-algebra/6167)

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**Author:** [@tkluck](https://discourse.julialang.org/u/tkluck)\
**Replies:** 10\
**Last updated:** [October 8, 2017, 4:06pm UTC](https://discourse.julialang.org/t/exact-linear-algebra/6167 "2017-10-08T16:06:54Z")

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Hey all! I’ve been using Julia for algebra computations (think polynomial rings, ideals, Groebner basis, etc). Linear algebra is often fundamental to that, and Julia seems very suited to that! There’s a few choices in …

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## [How to get DTable column names?](https://discourse.julialang.org/t/how-to-get-dtable-column-names/6307)

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**Author:** [@xiaodai](https://discourse.julialang.org/u/xiaodai)\
**Replies:** 1\
**Last updated:** [October 7, 2017, 12:26pm UTC](https://discourse.julialang.org/t/how-to-get-dtable-column-names/6307 "2017-10-07T12:26:19Z")

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I loaded a set of CSV using JuliaDB.jl’s loadfiles.And I got a DTable, but there does not appear to be a function that can tell me the names of the columns. There is a names functions for DataFrames it feels natural to …

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## [One stop shop for benchmark optimization problems?](https://discourse.julialang.org/t/one-stop-shop-for-benchmark-optimization-problems/6257)

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**Author:** [@mohamed82008](https://discourse.julialang.org/u/mohamed82008)\
**Replies:** 9\
**Last updated:** [October 6, 2017, 11:40pm UTC](https://discourse.julialang.org/t/one-stop-shop-for-benchmark-optimization-problems/6257 "2017-10-06T23:40:41Z")

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Wouldn’t it be nice to have a single package in Julia hosting benchmark optimization problems for different classes of optimization to make it easier for solver developers to test their solvers and benchmark them? The pr…

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## [Special method for Eigenvectors of Sparse+Hermitian+Complex matrix?](https://discourse.julialang.org/t/special-method-for-eigenvectors-of-sparse-hermitian-complex-matrix/6233)

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**Author:** [@Datseris](https://discourse.julialang.org/u/Datseris)\
**Replies:** 19\
**Last updated:** [October 6, 2017, 12:36pm UTC](https://discourse.julialang.org/t/special-method-for-eigenvectors-of-sparse-hermitian-complex-matrix/6233 "2017-10-06T12:36:44Z")

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After searching Google, the docs and discourse, I did not find any reference to any method that finds eigenvecs and eigenvals of Sparse, Hermitian and Complex matrices. I found a method specialized for Real and Symmetric…

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## [Parameters optimization profiles](https://discourse.julialang.org/t/parameters-optimization-profiles/6141)

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**Author:** [@ivborissov](https://discourse.julialang.org/u/ivborissov)\
**Replies:** 3\
**Last updated:** [October 6, 2017, 10:53am UTC](https://discourse.julialang.org/t/parameters-optimization-profiles/6141 "2017-10-06T10:53:27Z")

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Hi, has anyone solved the following optimization problem: I am estimating ODE parameters (using NLopt) like param1,param2,param3 and I want to create “profiles” of each parameter. It means estimate param2 and param3 for …

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## [HDF5: Writing to a Compound Table](https://discourse.julialang.org/t/hdf5-writing-to-a-compound-table/6265)

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**Author:** [@Jeremy](https://discourse.julialang.org/u/Jeremy)\
**Replies:** 0\
**Last updated:** [October 5, 2017, 3:46pm UTC](https://discourse.julialang.org/t/hdf5-writing-to-a-compound-table/6265 "2017-10-05T15:46:47Z")

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How do I write data to a compound table in an HDF5 file? I’ve figured out how to create the table. src = "/home/user/Desktop/hdf5\_test.h5" h5open(src, "w") do file cols = \["foo","bar","blah","blahblahblah"\] memtype\_…

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## [Reverting to earlier CUDA - version report stubborn](https://discourse.julialang.org/t/reverting-to-earlier-cuda-version-report-stubborn/6247)

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**Author:** [@Colin\_Beckingham](https://discourse.julialang.org/u/Colin_Beckingham)\
**Replies:** 3\
**Last updated:** [October 5, 2017, 9:57am UTC](https://discourse.julialang.org/t/reverting-to-earlier-cuda-version-report-stubborn/6247 "2017-10-05T09:57:53Z")

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I’m trying to revert versions of CUDA from 9 to 7. The removal of 9 and install of 7 seems to have gone ok but CUDAdrv.version() is still reporting v"9.0.0". I have Pkg.rm() twice each for CUDAdrv and CUDAnative and cle…

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## [Binary CUDA dependency](https://discourse.julialang.org/t/binary-cuda-dependency/6226)

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**Author:** [@una-dinosauria](https://discourse.julialang.org/u/una-dinosauria)\
**Replies:** 8\
**Last updated:** [October 4, 2017, 7:06am UTC](https://discourse.julialang.org/t/binary-cuda-dependency/6226 "2017-10-04T07:06:02Z")

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I’m in the process of building a Julia package which uses some custom CUDA kernels that I wrote a few years ago. I want to provide these CUDA binaries with the package, and have them compiled using BinDeps.jl. I’m follo…

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## [SQLAlchemy.jl Resurrected](https://discourse.julialang.org/t/sqlalchemy-jl-resurrected/6206)

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**Author:** [@ExpandingMan](https://discourse.julialang.org/u/ExpandingMan)\
**Replies:** 2\
**Last updated:** [October 3, 2017, 2:03pm UTC](https://discourse.julialang.org/t/sqlalchemy-jl-resurrected/6206 "2017-10-03T14:03:55Z")

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As complaining about SQL is one of my favorite pastimes, I’ve found that it made my life a whole lot easier to make SQLAlchemy.jl work again. So much work has been put into sqlalchemy that it seems crazy not to use it. …

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## [Julia DataFrames -\> plot 48 times slower than Python Pandas](https://discourse.julialang.org/t/julia-dataframes-plot-48-times-slower-than-python-pandas/6138)

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**Author:** [@johann.spies](https://discourse.julialang.org/u/johann.spies)\
**Replies:** 16\
**Last updated:** [October 3, 2017, 10:28am UTC](https://discourse.julialang.org/t/julia-dataframes-plot-48-times-slower-than-python-pandas/6138 "2017-10-03T10:28:09Z")

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I use the same methods and data in both Python and Julia (except that the Python plot has much more work as far as the attributes of the plot is concerned). I am fairly new to both Python Pandas and Julia DataFrames and…

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## [ANN: uCSV.jl](https://discourse.julialang.org/t/ann-ucsv-jl/6162)

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**Author:** [@cjprybol](https://discourse.julialang.org/u/cjprybol)\
**Replies:** 4\
**Last updated:** [October 3, 2017, 8:04am UTC](https://discourse.julialang.org/t/ann-ucsv-jl/6162 "2017-10-03T08:04:40Z")

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uCSV.jl is a µ-sized package for working with delimited text. The default behavior is similar to readcsv from base, but it is extensible enough to cover just about everything you’d expect from more established parsers in…

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## [How to open a graphics file on Windows using run()](https://discourse.julialang.org/t/how-to-open-a-graphics-file-on-windows-using-run/2955)

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**Author:** [@cormullion](https://discourse.julialang.org/u/cormullion)\
**Replies:** 6\
**Last updated:** [October 2, 2017, 4:50pm UTC](https://discourse.julialang.org/t/how-to-open-a-graphics-file-on-windows-using-run/2955 "2017-10-02T16:50:02Z")

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On macOS I can do this: run(\`open $(filename)\`) where filename might be image.png or /tmp/test.pdf or /Users/me/test.svg, and the file will open in Preview or Safari or whatever app you’ve decided to make the default f…

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## [Porting MLKernels.jl to Julia v0.6](https://discourse.julialang.org/t/porting-mlkernels-jl-to-julia-v0-6/6191)

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**Author:** [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Replies:** 2\
**Last updated:** [October 2, 2017, 3:12pm UTC](https://discourse.julialang.org/t/porting-mlkernels-jl-to-julia-v0-6/6191 "2017-10-02T15:12:28Z")

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I am finishing a PR for fixing MLKernels.jl in Julia v0.6. I got stuck with the following issue. Suppose I have code of the form: abstract type B{T} end abstract type C{T} \<: B{T} end struct D1{T} \<: B{T} end struct D2…

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## [JuMP Efficient Quadratic Objective Formulation](https://discourse.julialang.org/t/jump-efficient-quadratic-objective-formulation/6177)

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**Author:** [@Kenney](https://discourse.julialang.org/u/Kenney)\
**Replies:** 4\
**Last updated:** [October 1, 2017, 7:44pm UTC](https://discourse.julialang.org/t/jump-efficient-quadratic-objective-formulation/6177 "2017-10-01T19:44:13Z")

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Hi everyone, I (eventually) want to run an MIQP where the objective is a simple sum of squares say sum((Y-XB)^2). Without even getting to the constraints or the integer part of the problem, I’m running into issues simpl…

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## [Dynamical Systems API and ChaosTools.jl](https://discourse.julialang.org/t/dynamical-systems-api-and-chaostools-jl/4041)

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**Author:** [@Datseris](https://discourse.julialang.org/u/Datseris)\
**Replies:** 22\
**Last updated:** [October 1, 2017, 11:29am UTC](https://discourse.julialang.org/t/dynamical-systems-api-and-chaostools-jl/4041 "2017-10-01T11:29:35Z")

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I have recently started on a journey to create a package ChaosTools.jl that has common useful tools used in the study of nonlinear dynamics and chaos, like e.g. lyapunov exponents, attractor dimension estimation and othe…

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