Anonymous function returning NaN
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step 1) I have created a huge anonymous function, which I call funct. step 2) I calculated a position x3, which is 0.2. When I ask the type, it tells me it is a double, like this:
disp(x3)
x3 =
0.2
class(x3)
ans =
double
step 3) but when I evaluate the function, it gives me a NaN. Like this:
res = funct(x3)
ans =
NaN
What I dont get is, if I plot the function, it exists at 0.2, and is equal to -0.4. If I do the following:
x3 = 0.2 % the class is still double, and I check it
class(x3)
ans =
double
then it works:
res = funct(x3)
res =
-0.4
Anybody has a hint of why it didnt work in the first place? I need it to work inside a huge loop, and I get these NaN which breaks the code. Any help is appreciated.
采纳的回答
Star Strider
2015-3-25
0 个投票
We need to see the code for ‘funct’.
However, NaN is either the result of one of the values in a calculation being NaN, or more often, a 0/0 or Inf/Inf division. Check for those in ‘funct’.
更多回答（1 个）
John D'Errico
2015-3-25
Most probably, you THINK the original value is 0.2.
It looks like that after all. MATLAB displays it as such. But is it? Is it truly 0.2?
For example, it is trivial to give you a number that matlab will display as 0.2, but it is not so.
x3 = 0.2 + 1e-12
x3 =
0.2
Well, would you look at that! What a surprise.
x3 == 0.2
ans =
0
Next, it is equally trivial to write a function that will return a NaN for some values that are near 0.2, and a number that is not NaN for others. (Do I need to do this too?)
The point is, a NaN results from some computations, typically things that have an indeterminate result, like 0/0, inf/inf, inf-inf, or sin(inf). There are many ways it can happen, and I am sure I can come up with a few more quite easily.
You should check to see why it was created. So learn to use the debugger. Learn to use tools like dbstop, which can interrupt execution when a NaN is created.
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