How can I round off the coefficients of sys2 polynomial(num/den)?

num=[1 0 0];
den=[1 0 0 1];
sys=tf(num,den)
sysd=c2d(sys,0.3)
sys2=d2c(sysd)

[Walter Roberson]

For background, see http://www.mathworks.com/matlabcentral/answers/10096-i-m-trying-to-convert-a-system-from-c2d-and-then-from-d2c-but-the-results-are-not-the-same-why-the

[Paulo Silva]

Nice catch Walter :)

Answer 1

[Paulo Silva]

Hi sadel, I see another hard question :)

num=[1 0 0];
den=[1 0 0 1];
sys=tf(num,den);
sysd=c2d(sys,0.3);
sys2=d2c(sysd);
[num,den] = tfdata(sys2); 
num=round(num{:});
den=round(den{:});
sys2simple=tf(num,den)

Be carefull, in your example this code works well enough but please read the documentation about the round function!!!!!

Also take a look at round2

[Walter Roberson]

For example it seems to me that by the time a coefficient reaches 1/3, that the coefficient should be kept, rather than round it down to 0.

Paulo's code does what sadel asked, but I suspect it was not the right question to have asked.

[sadel]

Hi guys and thank you!!! I think I will use the "round2" function.

[sadel]

Ok I think now it's better, isn't it?

num=[1.5 0 0];

den=[1 0 2.3346 1];

sys=tf(num,den)

sysd=c2d(sys,0.3);

sys2=d2c(sysd);

[num,den] = tfdata(sys2);

num=round(num{:}/0.0001)*0.0001;

den=round(den{:}/0.0001)*0.0001;

sys2simple=tf(num,den)

[Paulo Silva]

yes it's good