Bode question

[Moorman]

 OK, this is a question born of ignorance. So laugh
 at it, chuckle at my lack of knowledge. But, answer
 it :-)

 I have never used MatLab for any work. I recently
 inherited some MatLab code. I downloaded the Windows
 version of Octave to see if the code would run.    
 (v 2.1.36)

 Everything is fine until the bode function is
 invoked. I then get a message that the first
 argument must be a system data structure.

 The bode command in the Matlab program is
 bode (a, b, c)

 a is a 180 x 1 matrix of real numbers
 b is a 180 x 1 matrix of complex
 c is a 180 x 1 matrix of complex

 I found some great help on using both matlab and
 octave, including particular invocations of bode
 in matlab. For example, one page suggested  
 the following test:

 num = [0.2 0.3 1]
 den1 = [1 0.4 1]
 den2 = [1 0.5]      

 den = conv(den1, den2)
 w = logspace(-1, 1, 50)

 [mag, phase] = bode(num, den, w) 

 When I try this, same error about the
 needing to be a system data structure.
 Now, I read the material on the internal          
 system data structure, but I am unsure what        
 to do :-(

 Again, I apologize for this question. I actually 
 feel so lacking of knowledge in this area that      
 I feel I am probably not even asking a reasonable  
 question. But, I had to try something before
 I go back to beating my head against the
 wall :-(

 Thanks for any insight you can shed or   
 pointers to what to read.

 Thanks,       
 Kenny






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