NaN for zero divide by zero.
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Will illustrate with an example, I.e:
a = (0:0.1:1); b = (1-a)*2./(1-a);
Matlab will output the end value in b as NaN, when in reality b should converge to 2 for a = 1.
How can I avoid this?
采纳的回答
Matt Fig
2011-4-6
0 个投票
There are two things to remember when looking at this problem.
1. A function having a limit as the independent variable approaches a point does not imply that the function value at that point is defined. You plugged in for the function value at that point. The fact that you get NAN says nothing about the limit of the function as the independent variable approaches that point.
2. NAN is the correct value when evaluating the function at that point. This is a standard double precision definition.
4 个评论
Stian Molvik
2011-4-6
Walter Roberson
2011-4-6
You will probably want to check out isnan()
Matt Fig
2011-4-6
Yes, if you know the limit, you can do
b(isnan(b)) = 2;
Stian Molvik
2011-4-6
更多回答（3 个）
Walter Roberson
2011-4-6
1 个投票
In order to avoid this, you will need to use the symbolic toolbox.
MATLAB is giving the correct numeric answer according to IEEE 754 floating point definitions. MATLAB works with actual values computed on real machines, not with limits or ideal values. See for example this portion of the FAQ
Sean de Wolski
2011-4-6
0/0 is the definition of a nan
doc nan
Stian Molvik
2011-4-6
0 个投票
1 个评论
Walter Roberson
2011-4-6
Try this:
sym a
b = (1-a)*2/(1-a);
and see what b contains afterwards.
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2011-4-6
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