McGill University
School of Computer Science

Computer Science COMP 199 (Winter term)
Excursions in Computing Science
We Know a Lot More than *Bleep*)

Instructor: T. H. Merrett

"Excursions in Computing Science" explores the role of computing in understanding the universe. So we link up theoretical science, mathematics and computing. Specifically, we look at some of the big ideas in science, such as quantum theory, special relativity, and gene expression; at the supporting mathematical concepts in linear algebra, mathematical logic, and nonlinear attractors; and at computing techniques including data structures, procedural abstraction, and object-orientation.

This course is a dance of science, mathematics and computing, with each of these subjects treated in novel ways, without prerequisites beyond high school.
(A CEGEP graduate may have seen some of the material before, but from a quite different approach.)

The science motivates the mathematics and the computing. The mathematics provides the concepts for the science and the formalisms for the computing. The computing gives experience with the mathematics and predictions for the science; later in the course, advanced computing applications are based on the mathematics. We can understand the science through mathematical analogies, which are better for abstract science than conventional analogies such as waves and particles. The mathematics captures the subtleties; the computing captures the complexities. The mathematics explains the science; the computing explains the mathematics.

The intention of the course is to to be a head start, by experiencing the abstractions by which we do science. We do this by progressing from the science from which the abstractions emerge, to the mathematics which explores the abstractions, to the computing which extracts the predictions and brings the abstractions back to science. Playing the three against each other gives a better grasp than looking at any one of them on its own. We do real science, real math and real computing. The novel way of looking at them will complement the detailed coverage of later, more advanced courses. You will encounter again the abstractions experienced here, and you will be ahead of the game by having experienced them.

                 For Grade Scholars and the Young at Heart

Week i Rules and Calculations                                                                     Notes PDF 202K
 Math: some neat numbers and rules for finding them; calculating with letters.
 Computing: programming your calculator or MATLAB makes it faster; graphics
       turns it into pictures.

Week ii Powers and Trees                                                         MATLABpak        Notes PDF 500K
 Math: numbers can get very big very fast or very small very fast.
 Science: from us to the universe in 9 steps; from us to smaller than the atom
       in 5 steps.
 Computing: searching by using trees upside-down.

Week iii Bases and Polynomials                                                   MATLABpak        Notes PDF 887K
 Math: counting on our fingers; decimals that go on forever; arithmetic on
       polynomials and why multiplication etc. work the way they do.
 Computing: counting on the computer's "fingers"
 Science: the genetic code.

Week iv Space Math                                                                                 Notes PDF 184K
 Math: arithmetic on matrices.
 Science: rotating and transforming space.
 Computing: matrices on the calculator and in MATLAB.

COMP 199                                         Excursions in Computing Science

                            COURSE SUMMARY

Part I Time and Spaces
The science discussed is quantum physics and special relativity, with
motivation from and applications to polarized light, quantum electrodynamics
and nuclear physics.
The mathematics covered is the linear algebra of (mainly) two-dimensional
vectors, matrices and tensors, and excursions into higher dimensions, especially
three-dimensional Clifford algebra.
A discussion of symmetry introduces the mathematics and many applications from
molecular vibrations, crystals and wallpaper to the electron structure of the
atom, quarks and the conservation laws of physics.
The computing aspect introduces array data structures and operations, functions
as procedural abstraction, some numerical linear algebra in the form of equation
solution, discussion of algorithm complexity and divide-and-conquer, and
applications to graphics, multimedia and Internet search engines. A guest
lecture introduces quantum computing.

Week 1 Polarized Light                                                                             Notes PDF 314K
 Science: building a scientific theory to predict by calculating;
        light through one, two and three polarizing filters.
 Math: trigonometry in a nutshell.
 Computing: programming with MATLAB.

Week 2 Operators                                                                MATLABpak          Notes PDF 173K
 Science: physical measurements and observations as operators;
        polarizing filter as projection.
 Math: vector and matrix products; projection and rotation operators;
       Pythagoras; linear operators.
 Computing: experiencing abstractions through programming; cost and
        complexity of algorithms.

Week 3 Speed of Light                                                           MATLABpak          Notes PDF 172K
 Science: there is a maximum speed for anything; laws of nature are not
        affected by uniform speed; lightspeed is a law of nature;
        the twin paradox.
 Math: fixed-point vectors of transformations; shear transformations;
        determinants; anti-Pythagoras.
 Computing: visualizing transformations by calculating them; procedural

Week 4 Two-dimensional Numbers and Turtles                                                         Notes PDF 184K
 Science: adding and multiplying arrows; is an imaginary dimension science?
 Math: rotations off the real line - right angle, any angle; the field axioms;
        multiplying rotations is adding angles - exponentials.
 Computing: turtle graphics.

Week 5 Particles with Periods                                                                      Notes PDF 125K
 Science: QED, the strange theory of light and matter; amplitudes and
        probabilities; amplitudes under particle exchange - fermions and bosons.
 Math: 2-numbers give particles frequencies, wavelengths and periods;
        approximate calculation.
 Computing: playing with consequences through programming; errors and artefacts
        of the computation itself.

Week 6 Spin                                                                                        Notes PDF 114K
 Science: polarization states of electrons; half-angles and walking dogs; two
        spin-1/2s make two qbits; two spin-1/2s make one spin-1; fermions and
 Math: matrices of complex numbers; anticommutativity.
 Computing: a preparation for quantum computing.

Week 7 Bonus lectures

 a) E=mc^2                                                                                         Notes PDF 136K
 Science: frequency and wavenumber transform like time and space; energy and
        momentum are frequency and wavenumber; units and dimensional analysis;
        classical limits - E = mc^2; conservation, anti-Pythagoras and nuclear
        fusion and fission; scattering light from electrons - the Compton
        effect; Doppler effect; equations of quantum mechanics.
 Math: practice
 Computing: (small) databases.

 b) invited lecture on quantum computing: Patrick Hayden                                           Notes PDF 76K

 c) Coordinates, angles and reality                                                                Notes PDF 170K
 Science: vectors are real - something is invariant as coordinate systems
        transform; some arrays do not transform like vectors; some real things
        do not transform like vectors; angles, reflections and rotations in 2D
        and 3D.
 Math: tensor products; Clifford algebra [PDF 103K].
 Computing: practice

Week 8  Higher dimensions: Sketchpad and Web page rank                          MATLABpak          Notes PDF 275K
 Science: constraint-based graphics for drawing and design; how important is a
        web page? Measuring personality. Surveying and GPS.
 Math: underdetermined and overdetermined linear equations - Lagrange
        multipliers and least-squares; linear approximations to nonlinear
        functions; optimization; eigenvectors and eigenvalues.
 Computing: iterative methods to find an eigenvector, gaussian elimination for
        solving linear systems; parallelization; Sketchpad [Postscript file on constraints in Sketchpad, 110K].

Week 8c Symmetry: Simplifying Matrices
(This is an extensive treatment of symmetry, a study rich in implications for
science and requiring challenging computations. It will require a couple of
months of dedicated effort, if you are starting from scratch, but this
treatment is self-contained and accessible to anyone prepared to do the work.
Prerequisites from other Weeks in this course are given explicitly when they
are needed.
 This "week" on symmetry was added in 2009 and is not intended, which earlier
Weeks are, to be covered in one week.)
     8c Part I Discrete symmetries and molecules                                MATLABpak          Notes PDF 1010K
 Math: the mathematics of symmetry - group theory; abstracting groups from
       matrices and then representing them back as matrices again.
 Science: vibrations of molecules.

     8c Part II Infinite symmetries and crystals                                MATLABpak          Notes PDF 1393K
 Math: infinite commutative groups in 1D and 2D; wallpaper - point groups and
       space groups.
 Science: waves; measuring CD track spacings and crystal atomic spacings.

     8c Part III Continuous symmetries and the atom                             MATLABpak          Notes PDF 1171K
 Math: rotational symmetry in 2D and 3D; commutators; spherical harmonics.
 Science: the electronic structure and fine structure of atoms.

     8c Part IV Abstract symmetries and lots of physics                         MATLABpak          Notes PDF 509K
 Math: commutator algebra; "special unitary" groups SU(2) and SU(3); Noether's
 Science: quarks; Lagrangian and Hamiltonian physics; symmetry and conservation
 Computing: cubic and quintic splines.

Week 9  Many Dimensions: Data Compression and Content                           MATLABpak           Notes PDF 125K
 Science: image compression and content analysis
 Math: orthogonal vectors in higher dimensions, complex roots of unity, 
	polynomial long division and remainders
 Computing: fast Fourier transform, divide-and-conquer

Part II Logic, Memory and Languages
The scientific aspect is the biology of gene expression. This is related to the
engineering of memory circuits in computers, which motivates this Part.
The mathematics is boolean algebra of logic and combinational circuits and the
nonlinear math of feedback loops and sequential circuits.
The computing covered is iterative techniques to find attractors and cycles in
feedback systems, automata for grammar recognition, expression evaluation, and
memory and state in high-level programming languages. A guest lecture introduces

Week 10 The laws of thought                                                                        Notes PDF 163K
Engineering: logic gates, combinational circuits such as adders for a computer,
        and circuit simplification using Karnaugh maps.
Math: axioms of boolean algebra, all possible unary and binary operators on two values,
        universal operators and reversible operators; proof by contradiction.

Week 11 Memory, feedback and automata                                           MATLABpak          Notes PDF 192K
Engineering and science: sequential circuits such as flipflops, control systems,
        gene expression and cell differentiation.
Math: (nonlinear) feedback loops of boolean circuits.
Computing: iteration, simple automata for language recognition, stacks and queues
        for expression evaluation.

Week 12 Memory and programming language: recursion and instantiation            MATLABpak          Notes PDF 269K
Science: the algorithmic beauty of plants.
Computing: grammars for operator precedence, fractal drawing, encapsulation and
        instantiation of state. (Notes on LISP HTML 3K)
Math: Mathematical induction and proving programs correct.

Week 13 invited lecture on bioinformatics: Mathieu Blanchette

Here is the version of this course taught in 2007 .

Handouts for the course can be found in directory ~cs199/handouts (not on the Web) by readers with accounts on the SOCS (McGill's School of Computer Science) system.

You are taking this course because you have
- a passion to know how the universe works and how to change it;
- a need to know this right now, not after the next course or after graduation or when you are as old as I am;
- enthusiasm for mathematics and science.

The course will try to
- answer all the questions you now have about science, math and computing;
  (Of course it won't succeed, but ask anyway and the course will get better.)
- leave you with more questions than it answered, so you know you will have lots more to learn during university and beyond;
- most important, allow you to experience the abstractions we use to understand the universe, just as you have, by touch and sight and sound,
   been experiencing the surface aspects of nature and artefacts, and came to university to learn more.

We will meet Mondays, Wednesdays and Fridays at 15:30--16:30.
Monday: lecture day. Wednesday: interaction day. Friday: presentation day.

There will be no examinations.
5% of the marks will be for your anticipating the lectures each week with a list, delivered by Sunday night,
            of questions and of excursions you would be interested to present.
80 % of the marks will be for work done in the Friday classes:
        35% for excursions which you will present;
        10% for handouts for your presentations;
        30% for your participation in presentations by others
20 % of the marks will be for a journal which you will keep and submit each Sunday.

Note on "experiencing abstractions".

As youngsters, we can experience electricity by trying to build electromagnets, radio by making a crystal set or becoming a ham operator, plants by growing them, animals by training pets, programs by writing them, etc. It is harder to experience the ideas of relativity, which characterize things that move incredibly fast; or of quantum physics, which looks at things incredibly small; or of the processes by which living cells reproduce, manufacture their proteins, make up various organs, play different roles in the body, and evolve, all of which is incredibly complicated.

These ideas are based on abstractions which themselves cannot be handled or experienced with the senses: trigonometry, complex numbers, linear algebra, mathematical logic, feedback systems and nonlinear attractors, even the secrets of processing and memory circuits hidden in integrated circuit chips. We can experience machines by sight and sound and touch, but can we comprehend the full potential of programs ("machines with no physical parts"), unrestricted by gravity, friction, corrosion, weather or wear and tear? I believe that we can experience these abstractions by exercising with the experiences we already have, that they are abstracted from. This course aims to build up chains of ideas of increasing abstraction and power by alternatively abstracting from experience then experiencing the abstraction.

I am grateful for enthusiasm, support and detailed comments variously from Omar Abdulhadi, Fahd Badran, Mathieu Blanchette, Luis Chaidez, Xiao-Wen Chang, Hossam El-Gindy, Frederic Guichard, David Harpp, Patrick Hayden, Don Hetherington, Solomon Li, Fred Mayer, Wolf Rasmussen, Kaleem Siddiqi and Jessica Thompson. Remaining errors and stubbornness are my own.

This course is dedicated to Albert John Coleman, who taught me first-year mathematics and much besides.