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Welcome back.

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I want to talk to you quickly about something called Matrix and a matrix is a way to describe 2D lists

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or multidimensional lists.

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What do I mean.

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Well I can create a matrix and this is a name that I just made so I can call it whatever I want but

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usually these are called Matrix in programming and it looks something like this.

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It's an array with another array inside of it so let's say for example

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I have one two three here and then another array one or listed two for six and then another array seven

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eight nine what's happening here.

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Well it's a two dimensional array.

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We have the main array and then we have sub arrays three arrays to be exact.

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Now why is this useful.

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And by the way this is two dimensional but we can have multiple ones.

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For example you can have another array inside of this array but why is this important these type of

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matrices come up a lot in topics like machine learning or image processing for example a computer doesn't

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really know what a photo of a dog is.

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The only thing it understands is zeros and ones.

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So a lot of photos for example let's say we had a very simple photograph of a giant X maybe this letter

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X well a computer can understand an image based on pixels on the screen.

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So maybe we can have 0 1 0 1 0 0 or sorry 1 here 0 here and then 1.

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And right now a computer can look at this and if this represented let's say a tiny little pixel here

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or maybe a pixel here or my screen the computer's going to say oh there's a one here.

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So that means I should make this green in this corner then dark here then green then dark green dark

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green dark green and a computer is able to draw let's say an X and this is a simple example and using

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matrices we can do a lot of these heavy calculations and that's how computers work underneath the hood

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when let's say for example it's trying to display something but the reason I wanted to talk about this

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here is when you want to access a multi dimensional list well you would do something like this let's

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say matrix access the first item in the matrix which in this case will be this first array because it's

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the first item and then let's say we want to access the zero in here or else change us to five.

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Well I'll do square brackets again and just do 0 1.

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So if I go one here and let's print that out

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and I click Run I get five.

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So it's accessing the first item in the array.

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So it's going to look at the first order array grab the first item which is right here and then grab

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the second item in that array.

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So 0 1 which is 5 and you can keep doing this if he had multi-dimensional arrays you can keep adding

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keep adding keep adding to access that information from an array or list.

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But remember in Python we want to use the term list I'll see in the next one.

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Bobby.