- `TF = isnan (X)`

Return a logical array that is true where the elements of `X` are `NaN` values.

Elements that are not `NaN` return false. In Octave, missing numeric values
such as `NA` are also considered `NaN` values.

See also: `isinf`, `isfinite`.

### References

- https://www.mathworks.com/help/matlab/ref/isnan.html
- https://octave.sourceforge.io/octave/function/isnan.html