MATLAB commands command window

As we have said before, en eers use formulas that represent physical and chemical laws governing our surroundings to analyze various problems. You can use MATLAB to input engineering formulas and compute the results. When typing your formula, use parentheses to dictate the order of operation. For example, in MATLAB s Command Window, if you were to type count=100+5 2, MATLAB will perform the muldplication first, which results in a value of 10, and then this result is added to 100, which yields an overall value of 110 for the variable count. If, however, you wanted MATLAB to add the 100 to 5 fiist and then multiply the resulting 105 by 2, you should have placed parentheses around the 100 and 5 in the following manner count=(100+5) 2, which results in a value of 210. The basic MATLAB arithmetic operations are shown in Table 15.3. 

To improve your understanding of the element-by-element operadons, in the MATLAB s Command Window type a = [743 —1] and b = [1, 3,5, 7] and then try the following... 

In the MATLAB s Command Window, we type the following commands. 

The help features and the Command Window interface tend to evolve quickly. For that reason, we use our Web Support to provide additional hints and tidbits so we can keep you update of the latest MATLAB changes. For now, we will introduce a few more basic commands ... 

MATLAB is most at home dealing with arrays, which we will refer to as matrices and vectors. They are all created by enclosing a set of numbers in brackets, [ ]. First, we define a row vector by entering in the MATLAB Command Window ... 

Save these statements in a file named, say, plotxy.m. Anything after the"%" sign is regarded as a comment, which you do not have to enter if you just want to repeat this exercise. After we have defined or updated the values of x and y in the Command Window, all we need is to enter "piotxy" at the prompt and MATLAB will do the rest. The key is to note that the M-file has no "read" or "input" for x and y. All statements in an M-file are simply executed in the Command Window. 

To launch the LTI Viewer, enter in the MATLAB command window ltiview... 

The LTI Viewer runs in its own workspace, which is separate from the MATLAB workspace. The Viewer also works with only LTI objects generated by functions such as tf () and zpk (), and after Chapter 4, state space objects, ss (). So let s generate a couple of objects in the MATLAB command window first ... 

Simulink shares the main MATLAB workspace. When we enter information into, say, the transfer function block, we can use a variable symbol instead of a number. We then define the variable and assign values to it in the MATLAB command window. This allows for a much quicker route to do parametric studies than changing the numbers within the Simulink icons and dialog boxes. 

To launch the root focus design tool, enter within the MATLAB command window ... 

In the previous sections we have used MATLAB commands that were typed in on the desktop command line, as well as MATLAB commands that invoke special stored MATLAB files, called m files. When starting to work with MATLAB, we advise our users to create a special folder for their personal MATLAB m files once and to continue to use this folder to store personal m files. To access the stored m files from the MATLAB desktop, the user has to point the small desktop window called Current Directory to the personal m file folder. Then all stored m files, as well as all built in MATLAB functions can be accessed, called upon, and used from the command line. All stored personal... 

MATLAB m files can contain any number of MATLAB commands. They are handy for long sets of MATLAB instructions or data and afford easy repeated use and easy modification. There are two kinds of MATLAB m files function and script m files. Script m files such as poly9. m on p. 28 use the data that is defined inside of them and any undefined data is taken from the data (with the proper name) that is currently active on the workspace look at the top left window commonly displayed on the MATLAB desktop for a list of defined variables and their type. Script files overwrite the workspace data as instructed in their code. 

There are many versions of Matlab and of Windows and for the more elaborate interfaces between die two packages it is necessary to refer to technical manuals. We will illustrate diis section with Matlab version 5.3, although many readers may have access to more up-to-date editions. All are forward compatible. There is a good on-line help facility in Matlab type help followed by die command, or follow the appropriate menu item. However, it is useful first to have a grasp of the basics which will be described below. 

These files are simple text files and may be created in a variety of ways. One way is via die normal Notepad text editor. Simply type in a series of statements, and store diem as a file with extension. m. There are five ways in which diis file can be ran from die Matlab command window. 

Open the m file, cut and paste the text, place into die Matlab command window and press the return key. The program should ran provided diat diere are no errors. 

Nonlinear algebraic equations can be solved using MATLAB, too. First, you have to define the problem to solve by writing a file called an m-file then, you check it finally, you issue a command to solve it. These steps are analogous to the steps used in Excel. You can use MATLAB most effectively if you learn to use the Command Window and learn to create m-files and save them properly. See Appendix B for additional details. 

Change the current directory in MATLAB (at the top of the command window) to a directory in which you wish to save your work and save it as f.m. 

Step 3 To find the value of x that makes/(x) = 0 in MATLAB, use the fzero function. In the command window, issue the following command ... 

Step 3 When using the global command, you must be sure to use the global command in the command window (or a run program that runs in the command window), set the variables after the global statement, and then repeat the global statement in the function. If you do not follow these mles, MATLAB will inform you that it was asked for an undefined variable or function, and give you the m-file and line number where it appears. 

Command Window This is where you enter variables and issue MATLAB commands. 

Command Histoty Window Shows the time and the date at which commands were is-sued during the previous MATLAB sessions. It also shows the history of commands in the current (acdve) session. 

Once in the ALATLAB environment, you can assign values to a variable or define the elements of a matrix. For example, as shown in F%ure 15.2, to ass a value of 5 to the variable X, in the Command Window after the prompt sign you simply type x = 5. The basic MATLAB scalar (arithmetic) operations are shown in Table 15.1. 

In the MATLAB Command Window, type the following commands as shown. x= 10... 

The MATLAB Command Window for Example 15.4 is shown in Figure 15.12. The plot of volume versus x is shown in Figure 15.13. 

In Secdon 14.8, plots of data points revealed that the teladonship between y and x is qua-dradc (second order polynomial). To obtain the coefficients of the second order polynomial that best fits the given data, we will type the following sequence of commands. The MATLAB Command Window for Example 14.11 (Revisited) is shown in F jire 15.27. 

The relative error vector x = [0.23076 0.17218 0.17253 0.14836 0.08526 0.01596], and enter this vector into Matlab and save (command save data x), and then in the MATLAB command window enter the following two lines and then pressing the Enter key ... 

In the MATLAB command window enter the following two lines after pressing the Enter key ... 

Type the following two lines in the MATLAB command window and then... 

The layout of MATLAB can be seen in Figure 4.1. There are a number of different layouts that the user can define, see Layout Tab. We select one basic layout that consists of the workspace, in the figure to the left top corner, where the variables are stored a command history, to the right bottom corner, where a log of operations is stored and the command window, where calculations can be executed. 

Needless to say that within MATLAB we have all the algebraic, statistical functions predefined along with plotting capabilities. Before briefly commenting on the basics, it is interesting to point out the use of help within the command window. We use the help function followed by any built-in function and MATLAB returns a small tutorial on the use of that function, the arguments, and the options (i.e., try help ode45 ). 

In this section the results of the measurements will be discussed. For the verification of the results a comparison model will be tacked. The comparison model is the transfer function of the low pass filter which is determined with the software tool Matlab. It will be execute measurements on the low pass filter and compared with result of the theoretical values. At firs the theoretical transfer function of the low pass filter will be plotted. This will be done over the following instruction on the command window of the Matlab tool. 

To start MATLAB, double click the corresponding icon, after a few moments the MATLAB Command Window will appear as shown in Fig. 8.1. In the command mode you can type a MATLAB command to which we will come back later. Now type Simulink. What appears is the Simulink library browser, as shown in Fig. 8.2. You now have various options to select building blocks for your simulatioa The blocks that are used mostly are in the following groups ... 

In a simulation, process parameters will be assigned mrmeric values. Rather than using these in the simulation, it is preferred to use variable names in the simulation and assign values to them in a separate file. To do so, select File, New, m-file in the Matlab command window. This opens the Matlab editor which enables you to assign values to parameters as shown in Fig.8.3. 

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