Hello I have a function for frequency analysis. I have equations something like on this link, http://www.mathworks.com/access/helpdesk/help/toolbox/control/ref/bode.html  first example, but whenever I copy that to look at it,  Undefined function or method 'tf' for input arguments of type 'double'. this error shows up, I cannot use the regular plot function, because i have imaginary number.
 

"Ongun Palaoglu" <ongun@mac.com> wrote in message <huutit$7pg$1@fred.mathworks.com>...
> Hello I have a function for frequency analysis. I have equations something like on this link, http://www.mathworks.com/access/helpdesk/help/toolbox/control/ref/bode.html  first example, but whenever I copy that to look at it,  Undefined function or method 'tf' for input arguments of type 'double'. this error shows up, I cannot use the regular plot function, because i have imaginary number.
>  

Hi Ongun, Do you have the Control System Toolbox?  That error indicates that you don't have tf.m in your installation. When you say that you have a function "something like" example one on bode.html, do you have a continuous system function?, or is it discrete?

If you have a system represented by a constant coefficient linear difference equation, you can use fvtool to visualize the frequency response.

Wayne

"Ongun Palaoglu" <ongun@mac.com> wrote in message <huutit$7pg$1@fred.mathworks.com>...
> Hello I have a function for frequency analysis. I have equations something like on this link, http://www.mathworks.com/access/helpdesk/help/toolbox/control/ref/bode.html  first example, but whenever I copy that to look at it,  Undefined function or method 'tf' for input arguments of type 'double'. this error shows up, I cannot use the regular plot function, because i have imaginary number.
>  

a hint:
- make sure you own and have properly installed the control system tbx...

     ver control;
% should yield a valid output...

us