# A Technical Blog

## Using julia -L startupfile.jl, rather than machinefiles for starting workers.

If one wants to have full control over the worker process to method to use is addprocs and the -L startupfile.jl commandline arguement when you start julia See the documentation for addprocs.

The simplest way to add processes to the julia worker is to invoke it with julia -p 4. The -p 4 argument says start 4 worker processes, on the local machine. For more control, one uses julia --machinefile ~/machines Where ~/machines is a file listing the hosts. The machinefile is often just a list of hostnames/IP-addresses, but sometimes is more detailed. Julia will connect to each host and start a number of workers on each equal to the number of cores.

Even the most detailed machinefile doesn’t give full control, for example you can not specify the topology, or the location of the julia exectuable.

For full control, one shoud invoke addprocs directly, and to do so, one should use julia -L startupfile.jl

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## Intro to Machine Learning with TensorFlow.jl

In this blog post, I am going to go through as series of neural network structures. This is intended as a demonstration of the more basic neural net functionality. This blog post serves as an accompanyment to the introduction to machine learning chapter of the short book I am writing ( Currently under the working title “Neural Network Representations for Natural Language Processing”)

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## TensorFlow's SVD is significantly worse than LAPACK's, but still very good

TensorFlow’s SVD is significantly less accurate than LAPACK’s (i.e. julia’s and numpy/SciPy’s backing library for linear algebra). But still incredibly accurate, so probably don’t panic. Unless your matrices have very large ($>10^6$) values, then the accuracy difference might be relevant for you (but probably isn’t). However, both LAPACK and TensorFlow are not great then – LAPACK is still much better.

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## Plain Functions that Just Work with TensorFlow.jl

Anyone who has been stalking me may know that I have been making a fairly significant number of PR’s against TensorFlow.jl. One thing I am particularly keen on is making the interface really Julian. Taking advantage of the ability to overload julia’s great syntax for matrix indexing and operations. I will make another post going into those enhancements sometime in the future; and how great julia’s ability to overload things is. Probably after #209 is merged. This post is not directly about those enhancements, but rather about a emergant feature I noticed today. I wrote some code to run in base julia, but just by changing the types to Tensors it now runs inside TensorFlow, and on my GPU (potentially).

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## JuliaML and TensorFlow Tuitorial

This is a demonstration of using JuliaML and TensorFlow to train an LSTM network. It is based on Aymeric Damien’s LSTM tutorial in Python. All the explinations are my own, but the code is generally similar in intent. There are also some differences in terms of network-shape.

The task is to use LSTM to classify MNIST digits. That is image recognition. The normal way to solve such problems is a ConvNet. This is not a sensible use of LSTM, after all it is not a time series task. The task is made into a time series task, by the images arriving one row at at a time; and the network is asked to output which class at the end after seeing the 28th row. So the LSTM network must remember the last 27 prior rows. This is a toy problem to demonstrate that it can.

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## JuliaPro beta 0.5.02 first impressions

JuliaPro is JuliaComputing’s prepackaged bundle of julia, with Juno/Atom IDE, and a bunch of packages. The short of it is: there is no reason not to install julia this way on a Mac/Windows desktop – it is more convenient and faster to setup, but it is nothing revolutionary.

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## Julia as a Glue Language

Julia is a great language for scientific and technical programming. It is more or all I use in my research code these days. It gets a lot of attention for being great for scientific programming because of its: great matrix syntax, high speed and optimisability, foreign function interfaces, range of scientific libraries, etc etc. It has all that sure. (Though it is still in alpha, so many things are a bit broken at times.) One things that is under-mentioned is how great it is as a “glue” language.

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## An Algebraic Structure For Path Schema (Take 2)


This is a second shot at expressing Path Schema as algebraic objects. See my first attempt. The definitions should be equivelent, and any places they are not indicates a deficency in one of the defintions. This should be a bit more elegant, than before. It is also a bit more extensive. Note that $R$ and $A$ are now defined differently, and $A^\ast$ and $R^\ast$ are what one should be focussing on instead, this is to use the free monoid convention.

In general a path can be described as a a hierachical index, onto a directed multigraph. Noting that “flat” sets, trees, and directed graphs are all particular types of directed multigraphs.

To repeat the introduction:

This post comes from a longish discussion with Fengyang Wang (@TotalVerb), on the JuliaLang Gitter. Its pretty cool stuff.

It is defined here independent of the object (filesystem, document etc) being indexed. The precise implementation of the algebric structure differs, depending on the Path types in question, eg Filesystem vs URL, vs XPATH.

This defintion is generally applicable to paths, such as:

• File paths
• URLs
• XPath
• JSON paths
• Apache ZooKeeper Paths
• Swift Paths (Server/Container/Psuedofolder/Object)
• Globs

The defintion whch follows provides all the the expected functionality on paths

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## An Algebraic Structure For Path Schema (Take 1)

Note I have written a much improved version of this. See the new post.

This post comes from a longish discussion with Fengyang Wang (@TotalVerb), on the JuliaLang Gitter. Its pretty cool stuff.

In general a path can be described as a a heirachical index. It is defined here independent of the object (filesystem, document etc) being indexed. The precise implementation of the algebric structure differs, depending on the Path types in question, eg Filesystem vs URL, vs XPATH.

This defintion is generally applicable to paths, such as:

• File paths
• URLs
• XPath
• JSON paths
• Apache ZooKeeper Paths
• Swift Paths (Server/Container/Psuedofolder/Object)
• Globs

The defintion whch follows provides all the the expected functionality on paths

more ...