T=1/get(input1,'freq');
input1 is a missing variable/object, so you'll have to figure that out. If this is is someone else's code, I have less information than you do about what it could possibly be.
for[i=0;1;1i<n;i=i+1];
{
% ...
};
I have no idea what language this is from, but it's not MATLAB. I am not familiar with any 4-argument for loop syntax, so I have no idea what the 1 means. You're using i as both an integer index and you're attempting to explicitly use it as a complex number. Both i and j are sqrt(-1). Unless you're using them as that, don't cause problems by overloading them for use as indices or something.
B=wn*T*sqr(1-1/4/Q/Q);
I'm assuming that's supposed to be sqrt()?
y=filter(input1,BB,AA);
Again, I'm assuming input1 is some variable you have already.
Without the missing variable, this is my best guess:
clc; clearvars
ymax=[ ];
ff=[ ];
fmin=1;
fmax=1000;
n=90;
qv=(fmax/fmin)^(1/n);
%T=1/get(input1,'freq');
T = 1/200; % fake number to make it run
Q=10;
for k = 0:n-1 % is this right?
fn=fmin*qv^k;
ff=[ff,fn];
wn=2*pi*fn;
A=wn*T/2/Q;
B=wn*T*sqrt(1-1/4/Q/Q);
b0=1-exp(-A)*sin(B)/B;
b1=2*exp(-A)*(sin(B)/B-cos(B));
b2=exp((-2)*A)-exp(-A)*sin(B)/B;
a1=(-2)*exp((-1)*A)*cos(B);
a2=exp((-2)*A);
BB=[b0,b1,b2];
AA=[-a1,-a2];
%y=filter(input1,BB,AA);
y=filter(BB,BB,AA); % just cram something in it so it runs
yy=max(y);
ymax=[ymax,yy];
end
