Numerical resolution of the TonerTu equations in cigar-shaped boxes ( Supplementary Information ). We define the aspect ratio of the boxes as = / , where is the width of the simulation box and is the length of the straight line joining the half-circles. Increasing the aspect ratio results in a transition from a flow field with a single +1 defect to flow fields hosting two vortices either separated by a +1 defect or two -1/2 defects. Each simulation has been repeated 50 times. As shown in b , the error bars correspond to the 95% confidence interval.
