How can I extract data members from stepinfo output in MATLAB?

Question

When the stepinfo function is run on a transfer function (i.e. stepinfo(tf)) a typical result is:

    RiseTime: 52.2052
SettlingTime: 85.4916
 SettlingMin: 0.9041
 SettlingMax: 1.0012
   Overshoot: 0.1192
  Undershoot: 0
        Peak: 1.0012
    PeakTime: 132.8773

I did some research into stepinfo. It appears it returns a struct. So I assigned the above result to a variable and checked its size using size(). It's a 1x1 matrix.

This has me pretty convinced that I cannot extract individual data members from this struct without first assigning it to a string and then performing string manipulations.

I need the Overshoot and PeakTime values, Does anybody know the best way to grab these values without using the P.O. and Tp formulas - and without a huge string mess?

Answer 1

Everything in MATLAB is considered a matrix. A single structure element (which is what is being returned by stepinfo in your example) is a 1-by-1 matrix of type struct. You can access the fields of your structure like so:

S = stepinfo(sys);        %# Returns a structure, stored in variable S
overShoot = S.Overshoot;  %# Get the value in the Overshoot field
peakTime = S.PeakTime;    %# Get the value in the PeakTime field

For more information about working with structures, check out this documentation page.