# DifferentialEquations.jl 2.0: State of the Ecosystem

#### May 8 2017 in CUDA, Differential Equations, HPC, Julia, Mathematics, Stochastics, Uncategorized | Tags: | Author: Christopher Rackauckas

In this blog post I want to summarize what we have accomplished with DifferentialEquations' 2.0 release and detail where we are going next. I want to put the design changes and development work into a larger context so that way everyone can better understand what has been achieved, and better understand how we are planning to tackle our next challenges.

If you find this project interesting and would like to support our work, please star our Github repository. Thanks!

Now let's get started.

## DifferentialEquations.jl 1.0: The Core

Before we start talking about 2.0, let's understand first what 1.0 was all about. DifferentialEquations.jl 1.0 was about answering a single question: how can we put the wide array of differential equations into one simple and efficient interface. The result of this was the common interface explained in the first blog post. Essentially, we created ... READ MORE

# Some Fun With Julia Types: Symbolic Expressions in the ODE Solver

#### May 4 2017 in Differential Equations, Julia, Mathematics, Uncategorized | Tags: | Author: Christopher Rackauckas

In Julia, you can naturally write generic algorithms which work on any type which has specific "actions". For example, an "AbstractArray" is a type which has a specific set of functions implemented. This means that in any generically-written algorithm that wants an array, you can give it an AbstractArray and it will "just work". This kind of abstraction makes it easy to write a simple algorithm and then use that same exact code for other purposes. For example, distributed computing can be done by just passing in a DistributedArray, and the algorithm can be accomplished on the GPU by using a GPUArrays. Because Julia's functions will auto-specialize on the types you give it, Julia automatically makes efficient versions specifically for the types you pass in which, at compile-time, strips away the costs of the abstraction.

This means ... READ MORE

# Building a Web App in Julia: DifferentialEquations.jl Online

#### January 17 2017 in Differential Equations, Julia, Mathematics | Tags: | Author: Christopher Rackauckas

Web apps are all the rage because of accessibility. However, there are usually problems with trying to modify some existing software to be a web app: specifically user interface and performance. In order for a web application to perform well, it must be able to have a clean user interface with a "smart" backend which can automatically accommodate to the user's needs, but also give back a nice looking response in under a second. This has typically limited the types of applications which can become responsive web applications.

Scientific software is one domain where user interface has been obstructive at best, and always in need of better performance. However, the programming language Julia has allowed us to build both an easy to use and highly performant ecosystem of numerical differential equation solvers over the last 8 months. Thus we had ... READ MORE

# 6 Months of DifferentialEquations.jl: Where We Are and Where We Are Going

#### December 15 2016 in Differential Equations, Julia, Mathematics, Programming, Stochastics, Uncategorized | Tags: DifferentialEquations.jl, julia | Author: Christopher Rackauckas

So around 6 months ago, DifferentialEquations.jl was first registered. It was at first made to be a library which can solve "some" types of differential equations, and that "some" didn't even include ordinary differential equations. The focus was mostly fast algorithms for stochastic differential equations and partial differential equations.

Needless to say, Julia makes you too productive. Ambitions grew. By the first release announcement, much had already changed. Not only were there ordinary differential equation solvers, there were many. But the key difference was a change in focus. Instead of just looking to give a production-quality library of fast methods, a major goal of DifferentialEquations.jl became to unify the various existing packages of Julia to give one user-friendly interface.

Since that release announcement, we have made enormous progress. At this point, I believe we have both the most expansive and flexible ... READ MORE

# Introducing DifferentialEquations.jl

#### August 1 2016 in Differential Equations, FEM, Julia, Programming, Stochastics | Tags: DifferentialEquations.jl, julia | Author: Christopher Rackauckas

Edit: This post is very old. See this post for more up-to-date information.

Differential equations are ubiquitous throughout mathematics and the sciences. In fact, I myself have studied various forms of differential equations stemming from fields including biology, chemistry, economics, and climatology. What was interesting is that, although many different people are using differential equations for many different things, pretty much everyone wants the same thing: to quickly solve differential equations in their various forms, and make some pretty plots to describe what happened.

The goal of DifferentialEquations.jl is to do exactly that: to make it easy solve differential equations with the latest and greatest algorithms, and put out a pretty plot. The core idea behind DifferentialEquations.jl is that, while it is easy to describe a differential equation, they have such diverse behavior that experts have spent over a century compiling ... READ MORE

# Optimal Number of Workers for Parallel Julia

#### April 16 2016 in HPC, Julia, Programming, Stochastics | Tags: BLAS, hyperthreading, julia, parallel computing, workers | Author: Christopher Rackauckas

How many workers do you choose when running a parallel job in Julia? The answer is easy right? The number of physical cores. We always default to that number. For my Core i7 4770K, that means it's 4, not 8 since that would include the hyperthreads. On my FX8350, there are 8 cores, but only 4 floating-point units (FPUs) which do the math, so in mathematical projects, I should use 4, right? I want to demonstrate that it's not that simple.

## Where the Intuition Comes From

Most of the time when doing scientific computing you are doing parallel programming without even knowing it. This is because a lot of vectorized operations are "implicitly paralleled", meaning that they are multi-threaded behind the scenes to make everything faster. In other languages like Python, MATLAB, and R, this is also the case. Fire up MATLAB ... READ MORE

# Interfacing with a Xeon Phi via Julia

#### March 4 2016 in C, HPC, Julia, Programming, Stochastics, Xeon Phi | Tags: C, julia, MIC, OpenMP, parallel, Xeon Phi | Author: Christopher Rackauckas

(Disclaimer: This is not a full-Julia solution for using the Phi, and instead is a tutorial on how to link OpenMP/C code for the Xeon Phi to Julia. There may be a future update where some of these functions are specified in Julia, and Intel's compilertools.jl looks like a viable solution, but for now it's not possible.)

Intel's Xeon Phi has a lot of appeal. It's an instant cluster in your computer, right? It turns out it's not quite that easy. For one, the installation process itself is quite tricky, and the device has stringent requirements for motherboard choices. Also, making out at over a taraflop is good, but not quite as high as NVIDIA's GPU acceleration cards.

However, there are a few big reasons why I think our interest in the Xeon Phi should be renewed. For one, Intel ... READ MORE

# What Exactly is Brownian Motion and Why Does it Matter?

#### January 19 2016 in Stochastics | Tags: biology, brownian motion, nonstandard analysis, stochastic differential equations, Wiener process | Author: Christopher Rackauckas

When you talk about randomness, stochastics, and noise, everything always seems to be going back to "Brownian motion" and "white noise". But what exactly are these things?

The problem is that if you ask someone who researches the subject, you most likely get many different definitions at the same time. The reason is because, although there are many equivalent definitions (and terms), every single one only seems to be a small part of the intuition of what this thing actually is. So I am going to state without proof equivalent formulations of , which is the same as , which is the same as ... READ MORE