[Windows] Backpropagation does not work

[mworchel]

When running the pose_estimation sample under Windows, the optimization part does not actually perform any optimization. The loss seems to vary randomly and the final estimate does not visually differ from the initial one:

It seems as if the parameter updates are not correctly computed (or are way too small since there is no visual difference between iterations) for whatever reason.

System:

• Windows 10 x64
• Python 3.7.4
• Redner 0.3.2 (CPU)

[mworchel]

I tested the pose_estimation sample in colab in both, CPU and GPU mode. The results are very different:

CPU:

GPU:

The CPU mode seems to have some convergence issues in general. Maybe deep down it's somehow related to the Windows backprop issue mentioned above.

@BachiLi Any idea, what could be the cause for the discrepancy?

[BachiLi]

Interesting. Looking into this.

[BachiLi]

CPU mode runs fine on my mac...I'm really confused.

[BachiLi]

It also runs fine on my linux machine. This seems like a Colab-specific issue?

[BachiLi]

This issue exists on Colab for all redner versions I tested. I have no idea why there is a discrepancy between Colab and my Linux machine.

[BachiLi]

This issue also exists on the Tensorflow side. Actually the tensorflow version crashes on Colab occasionally.

[mworchel]

Typical case of 'but it runs on my machine' :D That is really strange. Maybe has something to do with the type of CPU?

[BachiLi]

Yes, something is wrong on Colab.

[BachiLi]

I have a deadline next week and have to work on something else now. Please let me know if you find anything suspicious.

[mworchel]

Tested the pose estimation with my (custom) Windows GPU branch which is currently based on redner 0.2.3 and the backpropagation works without issues:

However, the CPU mode fails as above. So it really seems to be some CPU related issue that exists at least since 0.2.3.

I'll keep my eye open. Good luck with your deadline for now!