How to prevent rounding number

Hello everyone, I have a trouble about rounding. This is my example: I assign K=173.1227 but the numerator the transfer function G is 173.1. When I try K=173.227, the num of G is 173.2. How can I fix that? I try to format long and go to preferences to adjust the variable and command windows but that doesn't work. Please help me! TIA

Answer 1

[Walter Roberson]

G1 = tf(173.1227, conv([1 0.2], [1 8 20]))

G1 =
 
            173.1
  --------------------------
  s^3 + 8.2 s^2 + 21.6 s + 4
 
Continuous-time transfer function.

format long g
G1.numer

ans = 1×1 cell array
    {[0 0 0 173.1227]}

The transfer function itself is not using the rounded values. The rounded values are only for display purposes.

The internal code does not offer any way to configure the number of significant digits: it always uses %.4g format for non-integers.

[Hoang Le Tran]

Can I ask you a question about K? I use the command Margin to find the k neutral limitation. And I assign the K into the transfer function to test is the K right?.

G=tf([1],conv([1 0.2],[1 8 20]))

G =
 
              1
  --------------------------
  s^3 + 8.2 s^2 + 21.6 s + 4
 
Continuous-time transfer function.

K=margin(G)

K = 173.1227

But unfortunately, it is not right 100%. Can you help me?

[Walter Roberson]

Sorry, I am not familiar with margin or "k neutral limitation"

format long g
G=tf([1],conv([1 0.2],[1 8 20]))

G =
 
              1
  --------------------------
  s^3 + 8.2 s^2 + 21.6 s + 4
 
Continuous-time transfer function.

K = margin(G)

K = 
          173.122670692379

Answer 2

[FannoFlow]

Your data is still there, its just not printing out the full precision.

See also:

https://www.mathworks.com/matlabcentral/answers/1713455-how-to-reformat-the-display-output-precision-of-e-g-the-tf-function

K2 = 173.227;

K2 = 173.2270

G2 = tf([K2, conv(1, 0.2)], [1, 8, 20])

G2 =
 
  173.2 s + 0.2
  --------------
  s^2 + 8 s + 20
 
Continuous-time transfer function.

G2.numerator

ans = 1×1 cell array
    {[0 173.2270 0.2000]}

G2.denominator

ans = 1×1 cell array
    {[1 8 20]}

[Hoang Le Tran]

Thank you very much @Walter Roberson @FannoFlow. Perhaps, the value of k neutral limitation in transfer function is not exactly.

[Walter Roberson]

The calculations for the transfer function use the full precision of the values you use to construct the transfer function (or state space system)

Only the display of the transfer function is affected.