release fern model

Command:

python train.py \
  --dataset_name llff \
  --root_dir /home/ubuntu/data/nerf_example_data/nerf_llff_data/fern/ \
  --N_importance 64 --img_wh 504 378 \
  --batch_size 1024 --num_epochs 30 \
  --optimizer adam --lr 5e-4 \
  --lr_scheduler steplr --decay_step 10 20 --decay_gamma 0.5 \
  --exp_name fern

Profile

Profiler Report

Action              	|  Mean duration (s)	|  Total time (s) 
-----------------------------------------------------------------
on_train_start      	|  0.00023312     	|  0.00023312     
on_epoch_start      	|  0.00029521     	|  0.0088563      
get_train_batch     	|  0.00023997     	|  25.456         
on_batch_start      	|  6.1591e-06     	|  0.65317        
model_forward       	|  0.019652       	|  2084.1         
model_backward      	|  0.069537       	|  7374.4         
on_after_backward   	|  1.5543e-06     	|  0.16483        
optimizer_step      	|  0.0037302      	|  395.59         
on_batch_end        	|  0.00030407     	|  32.247         
on_epoch_end        	|  9.9102e-06     	|  0.00029731     
on_train_end        	|  0.00036468     	|  0.00036468