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MATLAB Basic Syntax Tutorial
Welcome to this matlab tutorial. This matlab tutorial is going to be on the basic syntax of matlab. So I’ve already opened matlab and this is generally the screen that you see most of the time. So the big main window’s called the command window, you’ll be working here most of the time. You can view your variables in the workspace on the bottom left, and you can view your current directory on the top left, and so that will tell you where in the file system you currently are. So, if you want to open a file from there you don’t have to type in the absolute path you can just type in the filename directly, or if you save a file that’s where it will go. So we call that the working directory and you can change the working directory to keep all your projects separate. So, you can go into the path up here and you know type in another path if you want to use the path for your particular project. So in matlab there are three basic types of numbers that you’ll be working with, or variables, that are all actually matrices. So you have scalars which are just plain numbers, you have vectors which is kind of like a list of numbers, and then you have matrices which are tables of numbers. So as I’ve mentioned before in matlab all these variables are represented as matrices. So if I do something like x = 5 you see that in a regular programming language you might just think of this as x = 5, but I can do something like check the size(x) and I see that it’s actually a 1 by 1 matrix. I can create a vector, we use square brackets, and you don’t need commas but I’m going to use them and so that creates a vector with the v = [1,2,3]; So if I do size(v) it’s a one by three vector, or you can also call it a one by three matrix. So this brings up some other interesting points about how matlab syntax works. I mentioned that you don’t actually need the commas so we can just do that and matlab knows that we want one by three matrix with the elements 123. So you also notice that I added this semicolon at the end of the line and what that does, it’s easier to see if I just don’t do it, so it prints out the last thing. So if I don’t use the semicolon it’s going to print everything out from the previous command, but if I do use the semicolon it will suppress the output. So, that’s why I didn’t put a semicolon after size(v). If I did I wouldn’t see anything. Now we’re going to go on to look at matrices, So it’s very similar to creating a vector except we need to have a way to separate each row, so that’s done with a semicolon and I’m not going to put one at the end so we can see the output. And so what that does is it creates a two by two matrix now with the elements 1234 in the variable A, and if I do size(A) it’s two by two. So those are the two things we’ve learned about initializing vectors and matrices that you can use commas to separate columns but you don’t need the commas you can just use spaces, and to separate rows you can use semi-colons. Another thing is that when you’re working with matrices and vectors
and you’re multiplying them and stuff like that, the dimensions of the vector are very important. So, typically you know you work with a column vector not a row vector like the one I just created, and so we can easily transform the previous vector which was a row vector into a column vector using an apostrophe and so that does a transpose. And so you see now that v used to be a one by three vector and now it’s a three by one column vector. You could have also initialized it using semicolons of course. Ok, so the next thing I want to talk about is how you can access elements of a matrix. Typically that’s done using parentheses and then indices and commas in between. So if I want to in general access the i row in the j column it would be a(i,j) So if I want a(1,1) for example I would do that. If I want a(1,2) and so on a(2,1), Another interesting thing you can do is access a vector within a matrix. So let’s say I want the first row of the matrix a, I can use the colon syntax to get the first row. So I’m going to put a 1 where I choose the row, and then I’m going to put a colon in the choice for column which means return me all the columns in row 1. So if I do that I get 1 2 which is the first world of A. Similarly I can use the colon syntax to get an entire column of A. So let’s say I want to choose the second row, or sorry the second column, so let’s say I want to choose the entire second column, I would do that. And of course if I do a colon in both parts of A it will just return me the entire A. So let’s create a bigger matrix now so I can better illustrate my next point. Alright, so I just created a four by four matrix. So the colon syntax can also be used to access ranges. So if I want I look at A it’s 1-16. If I want the part of A that has so a sub matrix that has the 6, 7, 10, 11 I could access that part by choosing the second and third row in the second and third column. If you’ve programmed before usually when you’re working with vectors, matrices, and arrays they’re zero indexed, in MATLAB it’s one indexed. So, a 1-1 returns me the first element, it’s not a 0-0. Another cool thing that we may use later is the colon syntax can be used all by itself it actually just creates a range. So if I did something like 1:10 gives me back all the numbers from one to ten, and so say I want to assign this to a variable, let me check the size of W, so that creates a row vector with the elements 1 to 10. It’s simpler to do than typing one through ten manually, right. So just to extend this a little bit we aren’t limited to only scalars, vectors, and matrices in matlab. You may have heard of a data structure called tensors, and so those are multi dimensional matrices, so it’s not a table it’s more like a cube or a hypercube. So you can instead of having a two by two matrix you can have a two by two by two tensor.
