Is this a bug in double precision data type?

2019 5 21
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更新时间：2019 5 21
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Try this
n=7; eye(n)*inf+ones(n)
I got
ans =
Inf NaN NaN NaN NaN NaN NaN
NaN Inf NaN NaN NaN NaN NaN
NaN NaN Inf NaN NaN NaN NaN
NaN NaN NaN Inf NaN NaN NaN
NaN NaN NaN NaN Inf NaN NaN
NaN NaN NaN NaN NaN Inf NaN
NaN NaN NaN NaN NaN NaN Inf
What I am expecting is the off-diaginal ones are 1's, rather than Nan's

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Dingyu Xue
Dingyu Xue 2019-5-21
Sorry I made a mistake. The answer is correct. To take the same effect, the infinite term inf should be made to a large finite value, say 1e30. The command should be
>> n=7; A=ones(n)+1e30*eye(n)

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Josh
Josh 2019-5-21

2 个投票

It's not a bug. What's happening is you're multiplying Inf * 0, which is undefined (it's equivalent to trying to calculate 0/0). Try something like this, it will just set the diagonal elements to Infinity without multiplying the off-diagonal elements by Infinity as well:
n = 7; diag(Inf * ones(n, 1)) + ones(n)

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