最近看代码，遇到一个函数isnan，网上找了很多资料没有发现有价值的，无奈之下只能阅读手册；

isnan

function:

Array elements that are NaN

description:

TF = isnan(A) returns an array the same size as A containing logical 1 (true) where the elements of A are NaNs and logical 0 (false) where they are not. For a complex number z, isnan(z) returns 1 if either the real or imaginary part of z is NaN, and 0 if both the real and imaginary parts are finite or Inf.

For any real A, exactly one of the three quantities isfinite(A), isinf(A), and isnan(A) is equal to one

估计大家还是没怎么明白，好的我现在举例说明：

1：

a=[0,1,2,NaN];

isnan(1./a);

result:

1 0 0 1

2:

a=[0,1,2,1];

isnan(0./a);

result:

1 0 0 0;

3;

a=[0,1,2,NaN];

isnan(a);

result:

0 0 0 1

好了大家是不是发现什么特别之处的啦，发现0和0，0和NaN，之间的乘除关系，结果isnan为logic 1(true),是的，这个是正确的，NaN的意思就是不是一个数，我们可以理解为无穷数。0/0就是NAN，NaN或者nan都是“非数”的意思，“0/0”、“∞/∞”、“0*∞”都会产生这种结果。好了我相信大家应该知道这个函数的用法了吧。