Mode collapse occurs when a GAN generator produces a narrow subset of possible outputs instead of covering the data distribution. The generator exploits an easy case—such as producing a convincing 0 repeatedly—and ignores other valid outputs. section 9.2 section 9.9
Recognize the failure through these practical signals:
- Outputs concentrate around the most common or easiest mode, even when the target distribution contains several modes. section 9.2
- A generator can fool the discriminator while producing little variety, because generating realistic data is harder than discriminating it. section 9.0
- A standard GAN may miss modes in a simple nine-cluster Gaussian grid, despite having only two output variables and ample network capacity. section 9.2
Testing a GAN on a nine-mode grid
Create nine separated two-dimensional Gaussian clusters, wrap them in a PyTorch TensorDataset and DataLoader, train a GAN, and plot generated samples with a KDE. Compare the generated density with the target grid: missing circles reveal mode collapse. section 9.2
WGAN-GP reduces mode collapse rather than eliminating it. It replaces the discriminator sigmoid output, uses a gradient penalty on interpolated real and generated samples, and makes the discriminator less likely to produce unusable gradients for the generator. section 9.3 section 9.3.3



