SD1.5 and SD2.1 not suitable for DDIM inverse

[shouwangzhe200]

I tried the code in playground_real.ipynb on SD1.4, SD1.5, and SD2.1, and found that the inverse process using DDIM can only generate images that are consistent with the original image for SD1.4. For SD1.5, the generated images have significant deviations, while for SD2.1, the reconstructed images through the inverse process completely collapse.