1.40.14613

1.50.17609

1.60.20412

1.70.23045

1.80.25527

1.90.27875

2.00.30103

Representing Poly nomials

MATLAB software represents polynomials as row vectors containing coefficients ordered by descending powers. For example, consider the equation

p(x) = x3 −2 x −5

To enter this polynomial into MATLAB, use the row of descending coefficients

p = [1 0 -2 -5];

Evalu ating Poly nomials

The polyval65H function evaluates a polynomial at a specified value.

To evaluate p at x = 5, use polyval(p,5)

ans = 110

Roots

The roots66H function calculates the roots of a polynomial: r = roots(p)

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r =

By convention, the MATLAB software stores roots in column vectors. The function poly67H returns to the polynomial coefficients:

p2 = poly(r)

p2 =

1 8.8818e-16 -2 -5

poly and roots are inverse functions, up to ordering, scaling, and roundoff error.

MATLAB Commands List

The following list of commands can be very useful for future reference. Use help in MATLAB for more information on how to use the commands.

Usualy commands both from MATLAB and from Control Systems Toolbox, as well as some commands/functions which we wrote ourselves are used. For those commands/functions which are not standard in MATLAB, we give links to their descriptions. For more information on writing MATLAB functions, see the function68H page.

Table 1. Command list

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Introduc tion to MATLAB Func tions

When entering a command such as roots, plot, or step into MATLAB what you are really doing is running an m74H -file with inputs and outputs that has been written to accomplish a specific task. These types of m-files are similar to subroutines in programming languages in that they have inputs (parameters which are passed to the m-file), outputs (values which are returned from the m-file), and a body of commands which can contain local variab. MATLAB calls these m-files func tions. You can write your own functions using function command.

Anew function must be given a filename with a ‘.m’extension. This file should be saved in the same directory as MATLAB software, or in a directory which is contained in MATLAB’s search path. The first line of the file should contain the syntax for this function in the form:

Function [output1, output2] = filename (input1, input2, input3)

A function can input or output as many variables as are needed. The next few lines contain the text that will appear when the help filename command is evoked. These lines are optional, but must be entered using % in front of each line in the same way that you include comments in an ordinary m-file.

Below is a simple example of what the function, add.m, might look like.

function [var3] = add(var1,var2)

% add is a function that adds two numbers var3 = var1+var2

If you save these three lines in a file called “add.m” in MATLAB directory, then you can use it by typing at the command line:

y = add(3,8)

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Obviously, most functions will be more complex than the one demonstrated here. This example just shows what the basic form looks like. Look at the functions created for this tutorial listed below, or at the functions in the toolbox folder in MATLAB software (for more sophisticated examples), or try help function for more information.

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