To start out, setup the open loop transfer function.
Next, you can choose to set up the MATLAB code in a few different ways. First make sure that both the numerator and denominator are in acceptable forms.
[1 2 3] is the same as saying
Using an example:
We can write the numerator and denominator MATLAB codes as:
For a more complex problem we can bypass the long and tedious expansion process and use the convolution function in MATLAB.
Here, the denominator is also represented by (s+1)*(s+3+3j)*(s+3-3j). Being three seperate parts, we can use convolution once for two of them, then use convolution again with the remaining part. Just look at the example:
conv( A , conv( B , C ) ) —> denominator = conv( [1 1], conv( [1 3+3*j], [1 3-3*j] ) );
After we define our numerator and denominator in MATLAB, we can use the root locus function then set our axis parameters as follows.
>>rlocus( numerator, denominator )
>>axis([-10 10 -10 10])
Your plot should look similar to the following for this example: