int2str returns the wrong result
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>> int2str(73167176531330624919225119674426574742355349194934)
ans =
73167176531330625585928818171611107149744948903936
Anyone know what's going on here? I'm guessing the number is too because when I evaluate the difference between the input and output, the answer is 0.
What causes Matlab to fill in nonsense numbers though?
1 Commento
Risposta accettata
James Tursa
il 8 Lug 2015
Modificato: James Tursa
il 8 Lug 2015
Your original number has too many digits to store in a double precision number. E.g.,
num2strexact(73167176531330624919225119674426574742355349194934)
ans =
7.3167176531330625585928818171611107149744948903936e49
So what you are seeing as output is exactly what is being stored (i.e., the exact decimal conversion of the binary bit pattern being stored), and there aren't enough mantissa bits in double precision to store more precision.
In fact, the nearest numbers in the double precision set to your original number are:
>> x = 73167176531330624919225119674426574742355349194934
>> num2strexact(x)
ans =
7.3167176531330625585928818171611107149744948903936e49
>> num2strexact(x+eps(x))
ans =
7.3167176531330635970522535241266364210737607344128e49
>> num2strexact(x-eps(x))
ans =
7.3167176531330615201335101101955850088752290463744e49
5 Commenti
James Tursa
il 8 Lug 2015
Well, you can't do a simple copy-paste since MATLAB will assume a double as you found out. So that means a bit more caution on your part. E.g., read as a string directly from the source, or copy-paste with manually adding the apostrophes, or copy-paste into a file and then read the file, etc.
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