Function sum_axis_keepdims 

pub fn sum_axis_keepdims(
    a: &Array<f64, IxDyn>,
    axis: Axis,
) -> FerrayResult<Array<f64, IxDyn>>

Helper: sum along an axis with keepdims semantics (keeps the axis as size 1).

This is useful as a func argument for apply_over_axes.

Errors

Returns FerrayError::AxisOutOfBounds if axis >= ndim.