EGR 102 Introduction to Engineering Modeling. Lab 05A Managing Data

Transcription

1 EGR 102 Introduction to Engineering Modeling Lab 05A Managing Data 1

2 Overview Review Structured vectors in MATLAB Creating Vectors/arrays:» Linspace» Colon operator» Concatenation Initializing variables Importing and exporting data 2

3 Review - Variables in MATLAB There are 3 major variable types recognized in MATLAB Scalar-a single value; one row and one column Vector-has either a single row or column of values Array or Matrix-has multiple rows and columns of values You can manually create arrays or vectors by using brackets, commas, and semicolons Brackets define the set of values, commas separate columns, and semicolons separate rows 3

4 Review - Arrays and Vectors Vectors and Arrays can be manually created with brackets, commas, and semicolons Always start and end with square brackets Each comma represents a different column, and each semicolon is a different row Using only one of these will give either a row vector or column vector Combining their use creates an array 4

5 MATLAB Structured Vectors Two methods to create ordered vectors with equal spacing: Built-in function linspace( ) -> USE when you know the number of elements Colon operator : -> USE when you know the interval between each element value (i.e., the step-size) 5

6 MATLAB Creating Vectors/Array linspace linspace() can give you a specific number of elements or values in a vector Entered as linspace(first_value,last_value,#_of_values) Will provide 100 values by default if a number is not specified Does so by using the following calculation: Step Size = Last Value First Value # of Values 1 6

7 MATLAB Creating Vectors/Array Colon Operator One other method of producing a structured vector is the colon operator, :. This method allows the user to specify the step-size in the vector being created FirstValue:Step-Size:FinalValue Uses a default step-size of 1 if not specified The last value actually in the vector may not be the same as the FinalValue entered The last value is whatever is the last value equal to or less than the FinalValue using the step-size 7

8 MATLAB Creating Vectors/Array Concatenation New vectors or arrays can also be created by combining previously existing ones through concatenation Just like when manually entering values, list the existing values and separate them with either commas or semicolons to create separate columns or rows of data 8

9 MATLAB Creating Vectors/Array Concatenation The order that the values are coded reflects the order that they will show up in the new variable The dimensions need to line up if there are multiple rows and/or columns Ex: One row cannot contain 4 values and the second have 6 9

10 MATLAB Creating Vectors/Array Concatenation Concatenation can also be used to create vectors and arrays. ConcatVec places Vec2 from the previous slide between the values 0 and 10 ConcatArray combines Vec1 and Vec2 as rows in what is now a 2x5 array instead of two vectors 10

11 MATLAB Creating Vectors/Array Concatenation Built-in functions can be utilized while concatenating. NOTE: Array creation from concatenation requires that the combined vectors have the same length. 11

12 MATLAB Initializing Values There maybe times when you want to initialize a vector or array in your code Basically create the variable and fill the space with placeholders These are replaced with actual desired values later in the code Can create a space of entirely ones or entirely of zeros with specified dimensions using one of the following commands ones(#_of_rows,#_of_columns) zeros(#_of_rows,#_of_columns) The command eye() can similarly be used to create identity matrices 12

13 MATLAB Importing Data Vector and Array data can be loaded into the MATLAB Workspace.txt Notepad.xlsx---- Excel.mat---- MATLAB Step 1: Save the file your current working folder in MATLAB Step 2: Load the data into the MATLAB environment using: Import wizard >> load( filename ) >> xlsread( filename ) Import Wizard is a tool that allows the user more control over what is imported but takes several steps load() and xlsread() are commands that simply load everything in the file 13

14 MATLAB Exporting Data Data can also be saved and exported from MATLAB This involves saving the variables from you work session as a.mat file and being available for later use There are several ways to save the variables. To save all variables: Use >>save( Desired_FileName ) Click on the save icon directly above the workspace To save individual variables: Right-click on the variables of interest and select the Save As option 14

15 Example Practice importing data using the file that has been provided on D2L Recorded_Data.xlsx Use both commands and the Import Wizard to try importing this data 15

16 Summary Review Structured vectors in MATLAB Creating Vectors/arrays:» Linspace» Colon operator» Concatenation Initializing variables Importing and exporting data 16