Why I have following error? unrecognized function or variable 'printsys'. Error at (line 5) printsys(num, den, 'z')

clear all;
clc;
num=[0 1 5 4]; % nominator values
den=[1 -4 1 -2.5]; % denominator values
printsys(num, den, 'z')
[r,p,k]=residuez(num,den); % partial fraction expansion
zeros=roots(num); % to find the zeros values
poles=roots(den); % to find the poles values

Answer 1

[Walter Roberson]

Change

printsys(num, den, 'z')

to

disp(tf(num, den, 'z'))

[Haziq Isa]

I download one of the toolbox it said, but still have the error said:

I don't get it, my lecturer only need "symbolic math toolbox". And I have download all the necessarry, but it still not recognized. Do i need to reinstall back the sofware?

[Walter Roberson]

residuez() is from the Communication Systems Toolbox.

roots() is from basic MATLAB.

printsys() is part of the Control System Toolbox, but does not appear to be indexed in the documentation any more. It is in the portion of Control System Toolbox functions marked as "obsolete"

help printsys

 PRINTSYS Print system in pretty format.
    PRINTSYS is used to print state space systems with labels to the
    right and above the system matrices or to print transfer functions
    as a ratio of two polynomials.
 
    PRINTSYS(A,B,C,D,ULABELS,YLABELS,XLABELS) prints the state-space
    system with the input, output and state labels contained in the
    strings ULABELS, YLABELS, and XLABELS, respectively.  ULABELS, 
    YLABELS, and XLABELS are string variables that contain the input,
    output and state labels delimited by spaces.  For example the 
    label string
        YLABELS=['Phi Theta Psi']
    defines 'Phi' as the label for the first output, 'Theta' as the 
    label for the second output, and 'Psi' as the label for the third
     output.
    
    PRINTSYS(A,B,C,D) prints the system with numerical labels.
    
    PRINTSYS(NUM,DEN,'s') or PRINTSYS(NUM,DEN,'z') prints the transfer
    function as a ratio of two polynomials in the transform variable
    's' or 'z'.
 
    See also: PRINTMAT and POLY2STR.

It is not part of the Symbolic Toolbox.

You can simulate it using the Symbolic Toolbox:

num=[0 1 5 4]; % nominator values
den=[1 -4 1 -2.5]; % denominator values
printsys(num, den, 'z')

    5*z + z^2 + 4
---------------------
z - 4*z^2 + z^3 - 5/2

function printsys(num, den, variable)
   sv = sym(variable);
   ns = char(poly2sym(num, sv));
   n_ns = length(ns);
   ds = char(poly2sym(den, sv));
   n_ds = length(ds);
   barlen = max(n_ns, n_ds);
   fprintf('%s%s\n', blanks(floor((barlen-n_ns)/2)), ns);
   fprintf('%s\n', repmat('-', 1, barlen));
   fprintf('%s%s\n', blanks(floor((barlen-n_ds)/2)), ds);
end

You might notice that the coefficients are not in the standard order, with the powers increasing and then the constant last. This is caused by the char() operation that converts the symbolic expression generated by poly2sysm() to a character vector for display. The output of poly2sym() by itself looks fine, but to get the spacing right according to printsys(), we have to convert to character vectors -- we cannot generate the correct length of fraction bar without converting to character vectors.

It is possible to write code that (A) puts the coefficients in the standard order; and (B) gets the spacing the same as is used by printsys(); and (C ) gets the spacing right for subtractions; and (D) omits the multiplications between the constants and the symbols. Possible. And if you care to do that... go ahead ;-)

But probably by far the easiest thing is to install the Control System Toolbox in order to either use printsys() or tf()

[Haziq Isa]

Thank you for your explanation really helpful.

Answer 2

[Yerson]

Unrecognized function or variable 'printsys'.

me aparece ese error que puedo hacer?

[Walter Roberson]

You do not have the Control System Toolbox installed.

Although printsys() is marked as obsolete, it is still present as of R2025a.