Finding self-locating loops in pi, receiving "Index exceeds the number of array elements. Index must not exceed 50."

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Gwilym
Gwilym 2023-6-1
评论： chicken vector 2023-6-1
Ran in:
Hi, as per title I came into this error. Is this related to memory or perferences perhaps?
% Define the number of digits to use from pi
numDigits = 100000;
% Load the first numDigits digits of pi into a string
piStr = num2str(pi, numDigits);
% Loop over all possible loop lengths
for loopLen = 1:floor(numDigits/2)
% Loop over all possible starting positions for the loop
for startPos = 1:numDigits-loopLen*2
% Extract the loop and the following sequence from piStr
loopStr = piStr(startPos:startPos+loopLen-1);
seqStr = piStr(startPos+loopLen:startPos+loopLen*2-1);
% Check if the loop appears again in seqStr
if contains(seqStr, loopStr)
fprintf('Found self-locating loop of length %d\n', loopLen);
fprintf('Loop starts at position %d\n', startPos);
fprintf('Loop sequence: %s\n', loopStr);
fprintf('Following sequence: %s\n', seqStr);
end
end
end
Found self-locating loop of length 1
Loop starts at position 18
Loop sequence: 1
Following sequence: 1
Found self-locating loop of length 1
Loop starts at position 21
Loop sequence: 9
Following sequence: 9
Found self-locating loop of length 1
Loop starts at position 31
Loop sequence: 4
Following sequence: 4
Index exceeds the number of array elements. Index must not exceed 50.

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回答（1 个）

chicken vector
chicken vector 2023-6-1
编辑：chicken vector 2023-6-1
Ran in:
The error comes from the fact that 50 is the maximum number of digits for pi.
You can have a proof of this by doing:
nDigits = 60;
num2str(pi, nDigits)
ans = '3.141592653589793115997963468544185161590576171875'
num2str(pi, ['%.' num2str(nDigits) 'f'])
ans = '3.141592653589793115997963468544185161590576171875000000000000'
Note that double precision floating point numbers have 16 digit of accuracy.
  1 个评论
Stephen23
Stephen23 2023-6-1
编辑：Stephen23 2023-6-1
50 is anyway well beyond the limits of double binary floating point:
3.141592653589793115997963468544185161590576171875 % 50 DOUBLE
3.141592653589793238462643383279502884197169399375105820974944 ... actual
% ^ oops
https://www.mathworks.com/help/matlab/matlab_prog/floating-point-numbers.html

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