Why am I getting an NaN value for my array?

Question

Greylyn Gao 2021-11-18

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https://ww2.mathworks.cn/matlabcentral/answers/1589439-why-am-i-getting-an-nan-value-for-my-array

回答： Walter Roberson 2021-11-18

n5 = [-5:5];
y0 = abs(Dn2f(0))
y0 = 0.5000
ys = abs(Dn2f(n5))
ys = 1×11
    0.0900    0.0000    0.1501    0.3183    0.4502       NaN    0.4502    0.3183    0.1501    0.0000    0.0900
function Dn = Dn2f(n)
    if n == 0
       Dn = 1/2;
    else
       Dn = (1-exp(-1j*pi*n/2))./(1j*pi*n);
    end
end

I specifically defined the value of my function at 0 because of a division by 0, and it even returns the correct value at 0 when I call it for a single value, but in an array, the value at 0 is NaN?

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Answer 1

Walter Roberson 2021-11-18

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https://ww2.mathworks.cn/matlabcentral/answers/1589439-why-am-i-getting-an-nan-value-for-my-array#answer_834274

In MATLAB if you test a non-scalar in an "if" statement, then the statement is considered true only if all of the outputs of the expression are non-zero. "if" does not act as a selector to only work on the elements that the test is true for.

You should learn how to use logical indexing.