Anonymous function returning either NaN or a real number depending if the input is a scalar or an element of a vector

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Adam Pigon 2016-10-12

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https://ww2.mathworks.cn/matlabcentral/answers/306963-anonymous-function-returning-either-nan-or-a-real-number-depending-if-the-input-is-a-scalar-or-an-el

评论： Adam Pigon 2016-10-15

I have the following problem: I have created a function f(a,b,c), where b and c are scalars and a is a vector, a = [1 2 3 4 5]. Function f returns 4 real values and for the last element of the vector it returns NaN. What is strange, when I supply the Input 'by hand' ie. f(5,b,c) it returns a real value but when I write f(a(5),b,c) it is NaN. It doesn't matter how long vector a is but if I change the value of the last element it can help. Has anyone encounered a similar problem?

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Steven Lord 2016-10-12

You should also post the result of the computation a(5)-5. My guess is that you're computing a and while the last element looks like it is exactly 5 that it is not, and is slightly larger leading to Inf or NaN values creeping into the calculation. When you pass in the exact value 5 you're right on the edge; when you pass in something just bigger than 5 you fall over.

Adam Pigon 2016-10-15

Dear All, I would like to thank you for your comments. Obviously, you were right - the last element of my vector a is actually not what it seems to be in the short format. Vector a was created as something like a = sqrt(x)^2 and a is not necessarily equal to x. Thank you for this hint!

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