Table of Contents

Giving a talk about algorithms

Below is some advice on how to prepare a talk/lecture in a seminar on algorithms.

Study the material

Find out how different parts of the material relate to each other. Ask yourself questions such as:

Plan the contents of your talk

Do not start making slides yet!

First decide what is the main message you want to get across. This is probably not that a certain problem can be solved in a certain amount of time: for that message you would not need to give a whole lecture. More likely you want to convince your audience of the effectiveness of a certain algorithmic design trick or a certain proof technique.

Now find out how to organize your talk around that message. Your talk will include at least:

  1. Introduction of the algorithmic problem (definition and motivation).
    • First get the audience interested: give an example that illustrates:
      1. why the problem is interesting (relevant for theory or practice);
      2. why the problem is non-trivial to solve.
    • Then define the problem more precisely and formally.
  2. Exposition and explanation of the solution.
    What building blocks do you need, and in what order will you present them?
    • First give an outline of the solution.
    • Then fill in the details of the building blocks.
      You will not have time to explain everything. Which proofs/details are relevant to your main message, and which proofs/details can you skip? Your main responsibility as a speaker is to make this selection. To be able to do so, you will need to have figured out many details yourself, you will need to understand the computations in the paper to see what precisely makes it all work etc. Now decide what to present to the audience, and what to skip or to tell only when somebody asks a question.
    • Then present/summarize the complete solution.
  3. Analysis and evaluation of the solution.
    • Analyse the solution.
    • Compare the solution to other solutions, lower bounds etc.
    • (Re)state your main message.

The order given above is not strict: take it as a starting point. Now check what is the main message you want to get across to your audience. How do you make sure they get the point? If you follow the order given above strictly and give your talk in such a way that the main message becomes clear only at the end of the talk, then there is a big risk. By that time the audience is in dire need of coffee and you may be running out of the time.

As an alternative, consider going through the above sequence in several cycles: the first time informally, sketchy, skipping lots of things, but including the main points you want to make. Then adding more precision, more detail, more understanding in one or two more cycles—each time focusing on different aspects but always repeating the main points.

In any case do not try to stuff too much content in your talk. Rather than trying to explain a lot of things in a hurry, it is better to explain a few things clearly and at ease with lots of examples. Think of examples you can use to illustrate your talk.

Work out the details and make your visual aids

Decide what visual aids you want to use. The options are usually computer presentations (made, for example, with IPE or PowerPoint), writing/drawing on the blackboard, physical models, and hand-outs.

Computer presentations

Main advantages: typewritten and therefore easy to read, good for animations, and if need arises, you can always return to previous "slides".

Bad: Better:
Propagation of signals is lazy. That means
that first all signals are loaded in the signal
buffer of the node they were initially inserted
in and propagate one level every time the
signal buffer is emptied.
* Insert signal in buffer of starting node;
* When buffer overflows, send signals one level up/down.

Some advice on design:

Black- or whiteboard

Main advantages: lots of space (so you can keep definitions and algorithms on the blackboard next to extensive illustrations); when you write or draw something on the blackboard, you direct the attention of your audience to exactly the right spot; the writing may keep you from going too fast for your audience.

Beware: preparing a blackboard talk takes as much time as preparing a computer presentation!

Physical models (made of paper, wood, plastic, rope etc.)

Main advantages: they can be truly three-dimensional, and the audience will remember!


Not an alternative for scarce space on the projection screen! The audience cannot study a hand-out and listen to you at the same time.


Make notes for yourself to use while giving your talk, but do not write your talk out word by word!
If you can answer questions and discuss the material with your fellow-students in English, then you can also give a talk in English without preparing it word by word. Don't be afraid of making errors while speaking: a speaker who talks to his audience and formulates freely with errors is still easier to understand than one who reads flawless English from paper in one go!

Practice, early!

Practice your talk. Do this early (you can already practice with rough paper sketches of your slides) because you may find that your talk needs to be changed substantially. While practicing:

Giving the talk

If you are short of time, skip things, finish with your main message, and finish on time.

Any comments on this text are welcome, please send them to Herman Haverkort.