science

Iliffe vector

Iliffe vector is a science 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 Iliffe vector rather than just read about it. In short: In computer programming, an Iliffe vector, also known as a display, is a data structure used to implement jagged arrays. Data structure An Iliffe vector for an n-dimensional array (where n ≥ 2) consists of a vector (or 1-dimensional array) of pointers to (n − 1)-dimensional arrays.

Key takeaways

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

Reference excerpt

In computer programming, an Iliffe vector, also known as a display, is a data structure used to implement jagged arrays.

Data structure An Iliffe vector for an n-dimensional array (where n ≥ 2) consists of a vector (or 1-dimensional array) of pointers to (n − 1)-dimensional arrays. They are often used to avoid the need for expensive multiplication operations when performing address calculation on an array element. They can also be used to implement jagged arrays, such as triangular arrays, triangular matrices and other kinds of irregularly shaped arrays. The data structure is named after John K. Iliffe. Their disadvantages include the need for multiple chained pointer indirections to access an element, and the extra work required to determine the next row in an n-dimensional array to allow an optimising compiler to prefetch it. Both of these are a source of delays on systems where the CPU is significantly faster than main memory. The Iliffe vector for a 2-dimensional array is simply a vector of pointers to vectors of data, i.e., the Iliffe vector represents the columns of an array where each column element is a pointer to a row vector. Multidimensional arrays in languages such as Java, Python (multidimensional lists), Ruby, Visual Basic .NET, Perl, PHP, JavaScript, Objective-C (when using NSArray, not a row-major C-style array), Swift, and Atlas Autocode are implemented as Iliffe vectors. Iliffe vectors were used to implement sparse multidimensional arrays in the OLAP product Holos. Iliffe vectors are contrasted with dope vectors in languages such as Fortran, which contain the stride factors and offset values for the subscripts in each dimension.

References

John K. Iliffe (1961). "The Use of The Genie System in Numerical Calculations". Annual Review in Automatic Programming. 2: 25. doi:10.1016/S0066-4138(61)80002-5.

Further reading "Chapter 3: Data Structure Mappings". Compiling Techniques. Associates Technology Literature Applications Society. Retrieved 5 May 2015.

Worked examples

Example 1 — a first encounter with Iliffe vector

Start with the simplest possible case. Write down what Iliffe vector claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Iliffe vector 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 Iliffe vector 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 Iliffe vector

In research: Iliffe vector appears in science 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 Iliffe vector 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: Iliffe vector is common in secondary-school and first-year university syllabi. It links to neighbouring topics Arrays, so understanding it makes those chapters shorter.
In everyday life: Look for Iliffe vector 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 Iliffe vector in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Iliffe vector 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 Iliffe vector out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Iliffe vector in simple terms?

In computer programming, an Iliffe vector, also known as a display, is a data structure used to implement jagged arrays. Data structure An Iliffe vector for an n-dimensional array (where n ≥ 2) consists of a vector (or 1-dimensional array) of pointers to (n − 1)-dimensional arrays.

Why does Iliffe vector matter?

Because it connects several science 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 Iliffe vector?

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 Iliffe vector.