while running an optimatization algo, m geting this error"matrix must be square"

the func tht is to be executed:

function [ E ] = Iden_4( a )
%UNTITLED Summary of this function goes here

%   Detailed explanation goes here
w=0:0.01:pi;
f=w/pi;

a1=[1 -0.9 0.81 -0.729]
a2=[1 0.04 0.2775 -0.2101 0.14]
d=freqz(a1,a2,w);
a3=[a(1) a(2) a(3) a(4)]
a4=[1 a(5) a(6) a(7) a(8)]
y=freqz(a3,a4,w);
E=sum((abs(y)-abs(d))^2)

[Alan Weiss]

Please mark your code with the {} Code button to help us read it more easily.

Alan Weiss

MATLAB mathematical toolbox documentation

[Matt J]

In future (see also Alan's remark), please font your code distinctly from your text using the {} Code toolbar button, as I have done for you now.

Regardless, you've omitted from your post how you are performing the optimization. You've also omitted the exact error message, which would reveal the line of code that generates it.