C2D Function

[Luke Trowbridge]

Hello:

 

When I execute the following code:

 

 

num = [5.0576e20, 0, 0, 0];

den = [1, 2.5296e4, 1.002247e9, 1.4011535e13, 2.1985832e17, 1.417505e21, 7.4138682e24, 1.588969e28, 1.6328178e31];

atf = tf(num, den);

dtf = c2d(atf, 1e-5);

 

 

Octave 3.2.4 and control package 1.0.11 return a sensible result for the variable dtf.  However, when the same code is executed with Octave 3.4.3 and control package 2.2.1, the value of the variable dtf is given as follows:

 

Transfer function "dtf" from input "u1" to output ...

y1:  0

Continuous-time model.

 

 

The C2D function seems to work fine in octave 3.4.3 if I use transfer functions with numerator/denominator coefficients that are a little close together (within 10^15).  How should I go about this continuous to digital conversion in octave 3.4.3?

 

Thanks for any help,

Luke Trowbridge