# How to prevent rounding number

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Hoang Le Tran on 16 May 2023
Commented: Walter Roberson on 16 May 2023
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

Walter Roberson on 16 May 2023
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 on 16 May 2023
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 on 16 May 2023
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

FannoFlow on 16 May 2023
Your data is still there, its just not printing out the full precision.
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 on 16 May 2023
Moved: Walter Roberson on 16 May 2023
Thank you very much @Walter Roberson @FannoFlow. Perhaps, the value of k neutral limitation in transfer function is not exactly.
Walter Roberson on 16 May 2023
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.

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