mathematics

NESL

NESL is a mathematics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand NESL rather than just read about it. In short: NESL is a parallel programming language developed at Carnegie Mellon by the SCandAL project and released in 1993. It integrates various ideas from parallel algorithms, functional programming, and array programming languages.

Key takeaways

NESL belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NESL to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NESL from memory before moving on to harder problems.

Reference excerpt

NESL is a parallel programming language developed at Carnegie Mellon by the SCandAL project and released in 1993. It integrates various ideas from parallel algorithms, functional programming, and array programming languages. The most important new ideas behind NESL are

Nested data parallelism: this feature offers the benefits of data parallelism, concise code that is easy to understand and debug, while being well suited for irregular algorithms, such as algorithms on trees, graphs or sparse matrices. A language based performance model: this gives a formal way to calculate the work and depth of a program. These measures can be related to running time on parallel machines. The main design guideline for NESL was to make parallel programming easy and portable. Algorithms are typically significantly more concise in NESL than in most other parallel programming languages, and the code closely resembles high-level pseudocode. NESL handles nested data parallelism by using the flattening transformation to convert nested data parallelism to flat data parallelism. This works by storing nested vectors as the nested data and a segment descriptor of vector lengths, separately. This flattening transform, however, can increase the asymptotic work and space complexity of the original program, leading to a much less efficient result.

Influences NESL heavily influenced Data Parallel Haskell.

Worked examples

Example 1 — a first encounter with NESL

Start with the simplest possible case. Write down what NESL claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to NESL before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about NESL ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of NESL

In research: NESL appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses NESL in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: NESL is common in secondary-school and first-year university syllabi. It links to neighbouring topics Array programming languages, Common Lisp (programming language) software, Concurrent programming languages, so understanding it makes those chapters shorter.
In everyday life: Look for NESL outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study NESL in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NESL means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain NESL out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NESL in simple terms?

Why does NESL matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study NESL?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on NESL.