Machine precision in simulink

Andy Bartlett - 2021-09-07T15:27:10+00:00

Question: Machine precision in simulink

I am currently working on simulink model.   One of the equations is "L = qf*(XL0+(XL1*alpha_quadrant))" where "alpha_quadrant" is constantly zero. "XL0" and "qf" are both constants. The result of the equation, when graphed, should be constantly -11.08, but as it can be seen in the picture the result keeps fluttering.

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Expert Answer

Kshitij Singh answered . 2025-11-20

format long g  % will shows higher precision than short, but can still hide some differences

a = 0.05;
b = a + eps(a);
c = a + 2*eps(a);
v = [c,a,b]      % the differences will not be visible in the command window

% converting to a string with 17 digits will be enough to see differences
mat2str(v,17)

% subtracting values is another way to make the differences visible in the
% command window
dv = diff(v)
max(dv)
min(dv)

The output of this code is:

v =
                      0.05                      0.05                      0.05
ans =
    '[0.050000000000000017 0.050000000000000003 0.05000000000000001]'
dv =
     -1.38777878078145e-17      6.93889390390723e-18
ans =
      6.93889390390723e-18
ans =
     -1.38777878078145e-17
     

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