i want to convert from direct to parallel form, and i am getting an error massage???

%H(z) coefficients  
[C,B,A] = dir2par([1 0 0 -1], [1 -0.8 0.37 -0.05])
n=[0:20] ;
%%%%delta function %%%%
[delta,n] = impseq(0,0,20); 
h = filter([1 0 0 -1], [1 -0.8 0.37 -0.05], delta); 
%%%impulse response h(n)%%%%%
h1 = 20*delta - 29.1765*(0.2).^n+10.1765*(((0.5).^n)*cos(0.9273)+0.88*((0.5).^n)*sin(0.9273));
%%%Difference 
difference = max(abs(h-h1)) 
####################

command window:

Undefined function 'dir2par' for input arguments of type 'double'.
Error in Untitled (line 3)
[C,B,A] = dir2par([1 0 0 -1], [1 -0.8 0.37 -0.05])

Answer 1

[Azzi Abdelmalek]

Download the function dir2par from here http://www.mathworks.com/matlabcentral/answers/?sort=asked+desc