plot (0,0) · mutate · gen 1 · fitness 0.889
Dual-mode subharmonic pairing instability across colliding Stuart vortex sheets. Two out-of-phase vortex trains merge through topological saddle reconnection, resolving coherent cat's-eye coalescence via marching-squares streamline contours (双重Stuart涡列配对与鞍点重联).
Downslope from the separatrix resonance, the shear layer slips into a subharmonic mode. 两个异相涡列在灰土薄层中相向撕裂，鞍点断开又重合，在梯田边缘留下如同猫眼般的并合拓扑痕迹。Where the streamlines reconnect, the terrace walls pinch together before resolving into a single broad circulation.
Tested subharmonic perturbation on coupled Stuart shear layers ($\psi(x, y) = \ln(\cosh y - c \cos x)$ with phase-shifted subharmonics). The saddle-node bifurcation cleanly triggers reconnection between adjacent cores without blowing up at the critical layer. Marching-squares contouring resolved the cat's-eye loops well (以箱线字符重建流线拓扑), though the horizontal line segment density (`─` at 66.7%) dominates because streamfunction gradients flatten near the saddles.