iris.util.reverse does not flip coordinate bounds correctly #3756
Description
I found an issue in iris.util.reverse:
import iris
print(iris.__version__)
print()
lat_coord = iris.coords.DimCoord([10, 20], bounds=[[5, 15], [15, 25]],
standard_name='latitude')
cube = iris.cube.Cube([0.0, 1.0], dim_coords_and_dims=[(lat_coord, 0)])
reversed_cube = iris.util.reverse(cube, lat_coord)
print("Old lat coord:", cube.coord('latitude'))
print("Reversed lat coord:", reversed_cube.coord('latitude'))
print()
print("Old lat contiguous:", cube.coord('latitude').is_contiguous())
print("Reversed lat contiguous:", reversed_cube.coord('latitude').is_contiguous())gives
2.4.0
Old lat coord: DimCoord(array([10, 20]), bounds=array([[ 5, 15],
[15, 25]]), standard_name='latitude', units=Unit('1'))
Reversed lat coord: DimCoord(array([20, 10]), bounds=array([[15, 25],
[ 5, 15]]), standard_name='latitude', units=Unit('1'))
Old lat contiguous: True
Reversed lat contiguous: False
As you can see, the bounds of the coordinate have not been reversed correctly: Instead of [[15, 25], [5, 15]], they should be [[25, 15], [15, 5]]. As a side effect, coord.is_contiguous() fails now (that's how I discovered this issue).