Transfer functions of data

Hi there,

I have a csv file that have 3 column that consists of 3000 data. Column 1 is time in ms. Column 2 is the data of first value datas. (Commanded velocity) Column 3 is the data of second value datas. (Actual Velocity)

I would like to do a transfer function of the first with second. and plot a bode plot then find the natural frequency.

what i did was below. I guess tf is not the first thing i should be using to do a tf of 2 sets of values. Anybody know what i should use?

if true
  % code
data = xlsread('data.csv');
Gc = tf(data(:,1),data(:,2)) 
<--- this is the part where it says the values of the "num" and den properties must be row vectors or cell arrays of row vectors, where each vector is nonempty and containing numeric data. 

end

[Azzi Abdelmalek]

can you be more clear?

what Gc = tf(data(:,1),data(:,2)) means

[Amazing Trans]

I want a transfer function between a input and output. column 2 is the input, column 3 is the output/actual value.

Answer 1

[Rajiv Singh]

If I understood the question, you want the transfer function between input, recorded in the second column, against y which is recorded in the third column. If so, you need a transfer function estimation function such as TFEST, or OE.

 Ts = data(2,1)-data(1,1); % assuming uniform time grid
 z = iddata(data(:,3), data(:,2), Ts)
 model = tfest(z, 2); % second order transfer function

http://www.mathworks.com/help/ident/ref/tfest.html

http://www.mathworks.com/help/ident/ref/oe.html