We provide a 5/4-approximation algorithm for the minimum 2-edge-connected
spanning subgraph problem. This improves upon the previous best ratio of 4/3.
The algorithm is based on applying local improvement steps on a starting
solution provided by a standard ear decomposition together with the idea of
running several iterations on residual graphs by excluding certain edges that
do not belong to an optimum solution. The latter idea is a novel one, which
allows us to bypass 3-ears with no loss in approximation ratio, the
bottleneck for obtaining a performance guarantee below 3/2. Our algorithm
also implies a simpler 7/4-approximation algorithm for the matching
augmentation problem, which was recently treated.Comment: The modification of 5-ears, which was both erroneous and unnecessary,
is omitte