为什么用k(k == NaN)= SomeNumber替换矩阵的NaN无效，其中k是要运算的矩阵 [英] Why does replacing NaNs of a matrix not work with k(k==NaN) = SomeNumber , where k is the matrix to be operated

问题描述

给出一个矩阵:-

k = [1   2   3  ;
     4   5   6  ;
     7   8  NaN];

如果我想用0替换数字(例如2)，可以使用:k(k==2) = 0.它可以正常工作，并给出以下预期答案:-

If I want to replace a number, say 2, with 0, I can use this: k(k==2) = 0 . It works correctly and gives the following expected answer:-

k =

     1     0     3
     4     5     6
     7     8   NaN

但是，如果我尝试替换NaN，为什么这不起作用，即k(k==NaN) = 0给出了这个信息:

But why does this not work if I try to replace NaN, i.e. k(k==NaN) = 0 gives this:

k =

     1     2     3
     4     5     6
     7     8   NaN

尽管我能够使用:k(isnan(k))=0达到期望的结果.但是为什么第一种方法不起作用?

Although I am able to achieve the desired result using: k(isnan(k))=0. But why does the first approach not work?

推荐答案

因为NaN==NaN是0.

不是数字等于不是数字?不是真的，它们不是数字，但不一定是同一件事.这是设计使然.

Not a number is equal to not a number? Not really, they are not numbers, but not necessarily the same thing. This is by design.

是0/0 == Inf-Inf吗?绝对不是.两者都是NaN.

Is 0/0 == Inf-Inf ? Definetly not. Both are NaN though.

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