Formatting A MATLAB Transfer Function (tf function)?

Question

I want to input a transfer function for a PI controller in MATLAB (and eventually do a Nyquist plot of it), which has the general form:

TF = [Kp + (Ki/s)] / [x + y + z ...]

My question is, if I am using the tf() function to plot in MATLAB, how do I get KI to be divided by s instead of multiplied by it? It seems to be pretty good at assigning the appropriate power of s when I just put in the coefficients, but I'm unsure how to tell it to divide by s even after reading the documentation.

Any help would be greatly appreciated, thanks!

Answer 1

Simple...

>> x=1    
x =

     1

>> y=2    
y =

     2

>> z=3    
z =

     3

>> s=tf('s')    
s =

  s

Continuous-time transfer function.

>> Kp=1    
Kp =

     1

>> Ki=3    
Ki =

     3

>> G=(Kp+Ki/s)/(x+y+z)

G =

  s + 3
  -----
   6 s

Continuous-time transfer function.