improvement for examples/mnist_forward_forward

[whubaichuan]

Context

Hi, I am running the examples/mnist_forward_forward, which is based on https://github.com/mohammadpz/pytorch_forward_forward as described in main.py. This example can be improved a lot.

Your Environment

• Installed using source? [yes]:
• Are you planning to deploy it using docker container? [no]:
• Is it a CPU or GPU environment?: GPU
• Which example are you using: examples/mnist_forward_forward
• Link to code or data to repro: https://github.com/pytorch/examples/blob/main/mnist_forward_forward/main.py

Expected Behavior

The test error is so high, not matching the results in FF paper. The lower the test error, the best the results, because test error is 100%-test accuracy.

Current Behavior

1. This code (examples/mnist_forward_forward) cannot produce the expect results as in Hinton's FF paper. I am using the torch==2.13.0 and torchvision==0.28.0 and get around 7% test error while in hinton' paper this should be around 1%-2% test error.
2. The base https://github.com/mohammadpz/pytorch_forward_forward shows that the test error is around 7%, which is not good.

Possible Solution

This repository can make the test error to 1% to 2 %, which is acknowledged by hinton in his previous homepge.

Steps to Reproduce

1. Just run https://github.com/pytorch/examples/blob/main/mnist_forward_forward/main.py, and the high test error would be reproduced.

Failure Logs [if any]