Confusion between real-world and floating-point values

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Life is Wonderful 2022-8-4

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1773620-confusion-between-real-world-and-floating-point-values

评论： Life is Wonderful 2022-8-4

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

Hello there,

I'm converting floating to real-world data values with the code snippet below.

I notice that after scaling, floating point values are no longer fractional, implying that data loss has occurred.

Thank you in advance

fi(linspace(-5,5,10),true,32,28)
ans = 
   -5.0000   -3.8889   -2.7778   -1.6667   -0.5556    0.5556    1.6667    2.7778    3.8889    5.0000

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 32
        FractionLength: 28
storedInteger(fi(linspace(-5,5,10),true,32,28))
ans = 1×10
   -1342177280   -1043915662    -745654044    -447392427    -149130809     149130809     447392427     745654044    1043915662    1342177280
storedInteger(fi(linspace(-5,5,10),true,32,28)) / 2 ^28
ans = 1×10
   -5   -4   -3   -2   -1    1    2    3    4    5

I'm expecting fractional length, but I'm wondering where it's gone. Thanks !!

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Answer 1

Walter Roberson 2022-8-4

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1773620-confusion-between-real-world-and-floating-point-values#answer_1020910

在 MATLAB Online 中打开

You forgot to take into account that an integer data type operated on with a double precision number, returns the integer data type

fi(linspace(-5,5,10),true,32,28)
ans = 
   -5.0000   -3.8889   -2.7778   -1.6667   -0.5556    0.5556    1.6667    2.7778    3.8889    5.0000

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 32
        FractionLength: 28
SI = storedInteger(fi(linspace(-5,5,10),true,32,28))
SI = 1×10
   -1342177280   -1043915662    -745654044    -447392427    -149130809     149130809     447392427     745654044    1043915662    1342177280
class(SI)
ans = 'int32'
SI / 2^28
ans = 1×10
   -5   -4   -3   -2   -1    1    2    3    4    5
double(SI) / 2^28
ans = 1×10
   -5.0000   -3.8889   -2.7778   -1.6667   -0.5556    0.5556    1.6667    2.7778    3.8889    5.0000