1: Introduction to Physics Computing and MatLabgallas/Lectures/1610_CompPrelimsMT_Le… · 1: Introduction to Physics Computing and MatLab ... will not teach you how to program computers

Dr. E Gallas

Oxford Michaelmas Term 2016

1: Introduction to

Physics Computing

and MatLab

Usual apologies

Computing Lab started in Week 1 … Lectures in Week 3 (?)

The schedule gods rule the schedule

Lectures about computing

will not teach you how to program computers

Learn by doing in the Computing Practical Lab

But also: Lots of fun/free interactive tutorials online !

These Lectures

Complement (not duplicate) online course material

But a bit about the Practical Lab & getting started with MATLAB

Describe (language independent):

Fundamental aspects of computers and computing

Programming guidelines and best practices

Some warnings and pitfalls

Motivate: just in case you are not excited already !

MT 2016 Computing -- Gallas 2

Before we get started

MATLAB is

computing environment and 4th gen. programming language

“proprietary” (www.mathworks.com) i.e. not ‘open-source’ Oxford-wide license for research/study Use Computing Lab Macs OR

Download MATLAB on your laptop: http://www2.physics.ox.ac.uk/it-services/categories/matlab

https://register.it.ox.ac.uk/self/software/

MATLAB Primary purpose: numerical computing

Strong user base: engineering, science, economics, …

Some MATLAB functionality highlights: Matrix manipulations

Plotting of functions and data

Implementation of algorithms

Creation of user interfaces

Can be interfaced to other languages (C,C++,Java, Fortran, Python)


MATLAB: “MATrix LABoratory”

http://www.mathworks.com/

http://www2.physics.ox.ac.uk/it-services/categories/matlab



https://register.it.ox.ac.uk/self/software/

http://www-teaching.physics.ox.ac.uk/computing/

Students work independently (no partners)

Keep your own logbook; Write your own code, programs

Objectives, material, deadlines

See the Prelims Handbook and links therein.

I notes the Deadlines here (as in the Handbook):

Michaelmas:

CO01 (late in/after week 7)

Advise: finish/mark ASAP (or before week 5)

CO02 (late in Hilary)

Advise: finish/mark before week 8 (last week of the Lab)

Hilary:

Choose one of the CO6x exercises (doom after week 7)

Advise: finish/mark before final weeks 6,7 to avoid queues


Computing Lab General




Computing Lab is OPEN ! weekdays during working hours Booking is not strictly enforced (generally open spaces found)

“Demonstrators” in the lab: help and assess !! Prelims Demonstrators are in the lab (for marking & help):

Thursday and Friday: 10:00-13:00 and 14:00-17:00

Bulletin board (in the Lab): Show demonstrator schedule and their pictures

How to: Ask for help or for getting marked in lab Get a demonstrator’s attention

Don’t be surprised if you have to wait

Continue working as far as you can at your computer

Demonstrators should get to you ~ in sequence

Alternative to Lab computers: Work on your own laptop Follow instructions for installing MATLAB

In the Computing Lab Practical Course webpage

Demonstrators: can’t really help sorting your laptop issues

In First year Computing, you must use MATLAB In Second Year: you may choose other languages (on request)


Computing Lab Operations

See the notice board In the Computing Lab

Demonstrators are

Happy to help

Ready to mark


Our Demonstrators:

Computing elements (1)


Compute input output


Computing introductions usually start with the evolution of logical signal processing hardware and storage … I just summarize here: • 1937: vacuum tubes • 1947 … 1955: transistors • 1958 … 1960: integrated circuit • 1970s: microprocessor

But to me: something more fundamental and useful in terms of computing software execution is the about time and clocks … so I start there …

2000 BC: Shadow clocks

300 BC - 1500:

Water Mechanical clock

1500: Spring powered clock

1656: Pendulum clock

(Huygens)

1930-1960: Quartz clock

1961 Atomic clock

MT 2016

Some Clock History

9 http://www.explainthatstuff.com/quartzclockwatch.html

Computing -- Gallas

http://www.explainthatstuff.com/quartzclockwatch.html

2000 BC: Shadow clocks

300 BC - 1500:

Water Mechanical clock

1500: Spring powered clock

1656: Pendulum clock

(Huygens)

1930-1960: Quartz clock *

1961 Atomic clock

MT 2016 Computing -- Gallas

Modern Computers: based on clocks

10

Fundamentally:

A Computer is a clock

The CPU (Central Processing Unit)

logic is driven by a clock

With every CPU clock tick, the CPU is

able to execute one instruction

+ logic

+ memory

Computers everywhere (1)


hilarioushumorfromouterspace.tumblr.com

newportoregon.gov/dept/npd/atmsafety.asp

.. From the obvious …

www.thecolor.com/Coloring/Bus.aspx

The principle is similar to that used by noise-cancelling headphones only the microphones and speakers used in automotive exhaust systems must be more powerful and capable of withstanding the intense heat and corrosive environment of an automobile exhaust.

Active Exhaust Noise Cancellation

The microprocessor monitors the

engine operation and/or the

acoustic frequencies propagating

in the exhaust pipe and generates

sound that is out-of-phase with the

noise generated by the engine.

… to the not

so obvious…

MT 2016 Computing -- Gallas 12 http://www.cvel.clemson.edu/auto/systems/active_exhaust_noise_cancellation.html

Time measurement clock technology (+ machine logic, storage): dramatic shift !

For the last few (~4) thousand years We used the most precise mechanical devices

available to measure time

In the last 50 years: We are using cheap / precise / high frequency clocks discovered

in the process of improving time measurement [+ logic + storage] to drive ever more precise mechanical devices !

We are amassing human knowledge on an unprecedented scale

And over the last ~20 years This has also enabled more “information” than ever before to be

available at your fingertips !

what comes next is what we make of it

our ability to “compute” is key to develop the systems we envision


Profound transition !

Computing

elements (2)

CPU : Central Processing Unit

Clock: ticks at “Clock Speed” or cycles per second (Hz)

Synchronizes all compute operations

Typical rate MHz - GHz (GHz: 1,000,000,000 ticks/second)

Its rate factors into performance of the CPU

HIGHER: ~Faster, but runs hotter, consuming more power

LOWER: ~slower, less costly, less power [longer battery life]

Logic: programmable input to the processor

Format called “bytecode” (“machine code” is another form)

Compilation converts your program code into “bytecode”

At each clock tick: process one instruction or piece of data

Memory: Stores “State” of machine at each point in time

For example: values of program variables


Compute

input output Clock

+ Logic

+ Memory

Details about CPU/processor/memory internals:

See www Outside the scope of this course !

We are here to learn “programming”


Computing

elements (3)

processor input output

program

memory

Instructions

‘State’

“bytecode”


How Matlab looks (GUI)

Command Window:

type commands here

What you’ve

stored

What you’ve

done

Files

Snapshots

exit

Type this in the Command Window

Press the ENTER or RETURN key

Restart if needed

This should always clear up catastrophic confusion

clear

For slightly less drastic problems

clears your storage without having to exit MATLAB

help

Type this followed by a command or function

These are also available in the menus


Most important MATLAB commands STAY CALM

AND

TRY AGAIN

There is no magic:

Even if it appears to work like magic

Back to the clock:

Computers do one thing at a time/clock tick

Clock is fast on a human scale ! Only seems simultaneous

Coded instructions are executed sequentially

Your program executes “top down” (one line at a time)

the next line can only know what has happened before it

We don’t write “bytecode”: We use “higher level languages” HLL (level level of abstraction from machine language)

Examples: Fortran, … C, C++, python, MATLAB, …

HLL syntax is built on lower level constructs:

Gives us a “shorthand” that hide the lower level constructs

More natural for humans readable (but still precise) code !

Note the implications:

One line of HLL code != one instruction for the CPU But the advantages far outweigh the disadvantages


Getting started …

A(ny) computing language

You are talking to a machine You cannot hurt its feelings

You are learning a new language Nouns: variables, class objects, …

Imply a thing

Verbs: operators, functions, … Imply an action

Statements combine the above Order within statements: dictated by syntax rules

Order of statements: determines your program logic Computers execute commands sequentially (think: clock !)

Computers do exactly and only what you tell them to do Using syntax as they understand it

Important to understand precisely the syntax, order

Computing language is very precise EVERY character is important


I really hate this darn machine;

I wish that they would sell it.

It won't do what I want it to,

but only what I tell it.

~Author Unknown

Best Language: Depends on intended application But also what’s trending is of interest

developing skill sets of general, marketable interest

The Most Popular Programming Languages of 2015 http://spectrum.ieee.org/static/interactive-the-top-programming-languages-2015


Programming languages

Simple statements:

assignment: A = 5;

call: CLEARSCREEN();

return: return 5;

assertion: assert(x > 0);

goto: goto next; beware !

Compound statements:

block: begin prompt('Number?'); readline(myNum); A=A*myNum; end;

do-loop: do (this) block1; while (that is true)

for-loop: do (this) n-times

if-statement: if (this1) block1; else (this2) block2;

switch: switch (c) { case 'a': alert(); break; case 'q': quit(); break; }

while-loop: while NOT EOF DO begin READLN end


Statement Overview (Note: not language specific)

Statements are the

• sentences and

• paragraphs

of our new language

Starting point for any development:

Decide Input / Output …

then we think about what happens in between (Compute) What are the INPUT(s) ?

What are the OUTPUT(s) ?


Computing

elements (4):

Example ATM


INPUT:

ATM card

PIN number

Choose service

Prompt for more …

OUTPUT:

Display

Service dependent:

Cash ?

Balance ?

Receipt ?

ATM card … or NOT !


Computing

elements (5):

Example ATM


Next time:

We build the “Compute” element

forming statements and blocks

and putting it all together !

Revelation starts with your first line of code

Computing Practical Lab: a good place to start

Today, I talked about

Computing Lab Basics, MATLAB

Clock history … how cheap / precise / high frequency clocks make modern computing possible

Why the clock is fundamental:

driving logical progression and outcomes

Higher Level Languages and “Bytecode”

Overview of Statements:

These are the sentences of computing languages

Next time … turning Statements into programs

Variables and scope, operators, logical blocks, loops, …

Best practices: for writing code and making plots


Summary Day 1


Documents

1: Introduction to Physics Computing and MatLabgallas/Lectures/1610_CompPrelimsMT_Le… · 1: Introduction to Physics Computing and MatLab ... will not teach you how to program computers