Function ptp 

pub fn ptp<T, D>(
    a: &Array<T, D>,
    axis: Option<usize>,
) -> Result<Array<T, IxDyn>, FerrayError>
where
    T: Element + PartialOrd + Copy + Sub<Output = T>,
    D: Dimension,

Range (peak-to-peak) of array elements over a given axis.

Returns max - min. Analogous to numpy.ptp(a, axis=...).

Errors

Returns FerrayError::InvalidValue if the array is empty.