Vectors-Accessing or Indexing Vectors by Toshant

Vectors-Accessing or Indexing Vectors by Toshant -...

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Accessing/Indexing Vectors For these notes, please assume the following definitions : vec = [45 11 37]; vec2 = [32 15 47]; 1. What is indexing? a. Indexing a vector is known as either changing the values in a vector or getting the values in a vector by referencing the position. b. x = vec(1) b.i. The line of code above goes to the 1 position in vec, and gets the value. In this case, it's 45. c. x = vec(45) c.i. The line of code above does not go to the value 45. It goes to the 45th position in the vector. Since there is no 45th position, matlab reads and error. 2. Assigning/Getting values of single positions. a. It's possible to change/get the single values in a vector. b. Accessing Values b.i. x = vec(1) b.i.1. The code above gets the value in the 1st position. In this case, x would become 1. b.ii. x = vec( i ) b.ii.1. The above is a general form. X will be set to the i-th value in the vector. c. Assigning values c.i. vec(1) = 60 c.i.1. The code above assigns 60 to the first value of the vector. Therefore, vec-> [60 11 37]. c.ii. vec(6) = 60 c.ii.1. The code above attempts to replace the value "45" in vec, and replace it with 60. But , remember that the value between the parenthesis refers to the position and not the value. c.ii.2. Matlab will go ahead and assign the 6th position in vec to 60. c.ii.2.a. But there's no 6th position? So what happens? c.ii.2.b. Matlab does not error. Instead, matlab will extend the vector to assign 60 to the 6th value. c.ii.2.c. With the code above, vec -> [ 45 11 37 _ _ 60] c.ii.2.d. You will notice that there are empty positions. What does matlab do? Well, it fills them in with zeros. c.ii.2.e.
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This note was uploaded on 02/28/2012 for the course CS 1371 taught by Professor Stallworth during the Fall '08 term at Georgia Institute of Technology.

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Vectors-Accessing or Indexing Vectors by Toshant -...

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