You now know a bunch about machine
learning. In this video, I'd like to teach
you a programming language, Octave, in
which you will be able to very quickly,
implement the learning algorithms we've
seen already and the learning algorithms
we'll see later in this course. In the
past I've tried to teach machine learning
using a, a large variety of different
programming languages, including C plus,
plus, Java, Python and Pi are. And also
octave and what I've found is that
students were able to learn the most
productively learn the most quickly and
prototype your albums most quickly using a
relatively high level language by octave
in fact What I often see in silicon valley
is even if you need to build if you want
to build a large scale deployment of a
learning algorithm what people will often
do is prototype in the language they
Octave which is a great prototyping
language so you can get your learning
albums working quickly and then only if
you need a very large scale deployment of
it only then spend your time
reimplementing the algorithms [inaudible]
some other language like that because one
of the lessons we've learned is that
programmer time or developer time that is
your time with the machine learning
[inaudible] time is incredibly valuable.
And if you can get your learning
algorithms to work more quickly in octave
then overall you have a huge time savings
by first developing the algorithms in
octave and then implementing [inaudible]
only after we have the ideas working. The
most common prototyping languages I see
people use for machine learning are
Octave. Mattlab-numpinr. Octave is nice
this is free open source and Mat-Lab works
well too but is expensive to many people
but if you have access to copy Mat-Lab you
can also use mat lab for this class if you
know [inaudible] or if you know R I do see
some people use it but what I see is that
people usually end up developing somewhat
more slowly in. You know more complete
languages [inaudible] syntax it's just
slightly [inaudible] clear than the octave
syntax and so because of that and because
we're releasing starter code in Octave I
strongly recommend that you not try to do
the pony exercises in this class in Empire
R but that I do recommend that you instead
do the pony exercises for this class in
octave instead. Welcome to do this video
is go through a list of commands very,
very quickly and goes will quickly show
you the range of commands and the range of
things you can do in office. The course
web site we have a transcripts of
everything I do and so after watching this
video you can refer to transcript person
in the course web site when you want to
find a command. Our feel free whatever
recommend you do is fresh wash and after
watching Now DDN then is [inaudible]
octave on your computer and finally it
goes to the course website download the
transcripts of the things you see in this
section and type in whatever commands seem
interesting to you into octaves
[inaudible] on your own computer so that
you can see it for yourself. And, with
that let's get started. Here's my Windows
desktop, and I'm start in Octave. And I'm
now in Octave and, and there's my Octave
prompt. Let me first show you the
elementary operations you can do in
Octave. So, you can type in five plus six,
that gives you the answer of eleven. Z
minus two. Five times eight. One over two.
Two to the power of six. Is 64. So that
the [inaudible], elementary, math
operations. You can also do logical
operations. So one=2 of this evaluation
that follows. The percent command here is,
means a comment. So one=2, evaluates the
[inaudible], which is represented by zero.
One [inaudible]= to two. This is true, so
that returns one. You know that a not
equal sign is this. To their equals symbol
and not bang equals which some of the
[inaudible] languages use. The theological
operations one and zero use a double
ampersand sign to denote the logical and.
That evaluates the false, one or zero, z
or operation. And that evaluates the true.
And I can x over one and zero, and that
evaluates the one. This thing over on the
left, this Octive 324 [inaudible] eleven,
this is the default Octive prompt. It
shows what version of Octive and so on. If
you don't want that prompt, this is
somewhat cryptic to come on. Quote
particular then and so on that you can use
to change the prop and I guess this quoted
string in the middle you know quote
greater than greater than state, that's
what I prefer my octave prompt to look
like, so if I hit enter, oh excuse me,
like so, PS1 like so now my octave prompt
has changed to the greater than greater
than sign which you know looks quite a bit
better. Next lets talk about octave
variables. I can take the variable A and
assign it to three and hit enter. And now
A is equal to three. You want to sign a
variable but you don't want to print out
the result if you put a semicolon. The
semicolon. Suppresses, the, print, the,
the print output. So to do that enter, it
doesn't print anything. Whereas A=3, you
know, makes it printed out. Whereas A=3;
doesn't print anything. I can do string
assignment, B=high. If I just enter b, it
prints out the variable b. So b is the
string high. C equals three grade integral
one. So now c evaluates the true. If you
want to print out a display of your
variable, here's how you go about it. Let
me set a equals pi. And, if I wanna print
A, I can just type A, like so, and it
prints it out. For more complex printing,
there's also the [inaudible] command,
which, sends the displays. [inaudible]
display A, it just prints out A like so.
You can also display the strings, so
[inaudible] F, two decimals. And percent
0.2f, a like so. And this will print out
the string two decimal colon 3.14. This is
kind of a [inaudible] old style C-syntax.
For those of you that have program C
before this is [inaudible] syntax used to
print strings. So sprintf generates a
sprint, generates a string. Does this and
two decimals 3.1 pulls the string this
percent 0.2F means substitute A into here
showing it with two digits after the
decimal point and this takes the string
this generated by the sprint F command S
print f the sprint F command and this
actually displays the string and to show
you an example, sprint F six decimals. >>
Percent 0.6F comma A. And this should
print pi with six decimal, to, to, six
decimal places. Finally, I'll explain A
like so, look like this, there, there are
useful shortcuts you take, formats long,
it causes strings to, by default, be
displayed to a lot more decimal places,
and format short [inaudible] default of
just printing a small number of digits. >>
Okay. That's how you work with variables
now lets look at vectors and [inaudible]
let's say you want to assign A to matrix
let me show you an example, twelve:34: .
Five, six. This generates a three by three
matrix A who's first row is 1,2, second
row three, four, third row is five, six.
What the semi colon does is essentially
say go to the next row of the matrix.
There are other ways to type this in. Type
angles one, two semi colon. Three, four;
five, six, like so. And that's another
equivalent way of assigning A to be the
values of, this, three by two matrix. Some
[inaudible] assign factors. So V=1, two,
three. This is actually a [inaudible]
vector. Or this is a three by one vector,
right? This is a [inaudible] Y vector,
excuse me. Not, this is, a one by three
matrix. Right not N by one if I want to
assign this to a. Harden factor. What we
do instead is B equals one semicolon, two
semicolon, three and this will give me a.
Three by one is one by three vector so
this is a column vector. Here some more
useful notations b equals one colon 0.1
colon two. What this does is it sets b to
the bunch of elements that start from one.
And increments and, and steps of 0.1 until
you get up to two. So if I do this, V is
going to be this you know, low vector. Or
this is what, one by eleven matrix really.
That's 1.1, one, 1.1, 1.2, 1.3 and so on
until we get up to two. Now and I can also
say B = one:6 and that sets B to be these
numbers one through six. Okay now here's
some other way to generating matrices, 1's
2x3 is a command that generates a matrix
that is a 2x3 matrix that is the matrix of
our 1's so if I set C = two x 1's 2x3 this
generates a 2x3 matrix that is all 2's and
this is you can think of this as a shorter
way of writing this NC = 222 semicolon 222
which will also give you the same result.
Lets say W = 1's, 1x3 so this is going to
be a row vector or a you know row of three
1's and some of you, you can also say W =
0's 1x3 this generates a matrix, 1x3
matrix, of all 0's. Just a couple more
ways to generate matrixes. There I do W
equals rand one by three. This gives me a
one by three matrix of all random numbers.
If I do rand. Three by three excuse me a
three by three matrix of all random
numbers drawn from the uniform
distribution which is 01. So every time I
do this I get a different set of random
numbers drawn uniformly between the zero
and the one. For those of you who know
what a Gaussian random variable is or for
those who know what a Normal random
variable is you can also say that W called
rant N one-third. So these are going to be
three values drawn from a Gaussian
distribution which means zero and variance
distribution is equal to one. And. Can set
more complex things like W = -six plus
square root ten. Times. Let say rand
[inaudible] one by 10,000. [inaudible]
semicolon at the end because I don't
really want to [inaudible] it out. This is
going to be a what. Well this is going to
be a vector of 100,000 [inaudible] 10,000
elements so. Well actually you know what
let's print it up so this would generate a
matrix like this Right? With 10,000
elements so that's what W is. And if I now
plot a histogram, W, with the hiss command
I can now enter [inaudible]. Hiss command
takes a couple seconds to bring these up
but this is a histogram, my random
variable for W that was minus six plus
zero ten times this Gaussian random
variable. And I can plot a histogram with
more buckets, with more bins, with say 50
bins and. This is my histogram of
[inaudible] with mean - six because I have
a -six t here plus [inaudible] ten times
so the, the variants or this calcium is
therefore ten on the standard deviation
the square root of ten which is about what
3.1. Finally one special command to
generate a matrix which is the I command
so. I stands for, this is maybe pun on the
word identity. But so they set i4, this is
the four by four identity matrix. And I,
of course i4, this gives me a four by four
identity matrix and I [inaudible] i5, i6,
that gives me a six by six identity
matrix, as i3 gives the three by three
identity matrix. Lots of these are
[inaudible] has one more useful command
which is the help command. So you can type
help I, and this brings up the help
function for the identity matrix. Hit Q to
quit and you can also type help rand
brings up documentation for the rand or
the random number generation function or
even help, help which shows you help on
the help function. So, those are the basic
operations in octave and with this you
should be able to generate a few matrices,
multiply, add things, and, and use the
basic operations in octave. In the next
video, I'd like to start talking about
more sophisticated commands and how to
move data around and start to process data
in octave.