What is the parameter "num_samples_cls"? about classifier-balancing HOT 1 OPEN

I found num_samples_cls determines how many samples of one class would present in a batch.
I tried with num_classes=20, batch_size=10 and num_samples_cls=4.
Following is the printed sampled label_id of 5 batches:
batch 1: [15, 15, 15, 15, 7, 7, 7, 7, 9, 9]
batch 2: [9, 9, 0, 0, 0, 0, 4, 4, 4, 4]
batch 3:[17, 17, 17, 17, 1, 1, 1, 1, 6, 6]
batch 4:[ 6, 6, 5, 5, 5, 5, 11, 11, 11, 11]
batch 5:[16, 16, 16, 16, 3, 3, 3, 3, 18, 18]
Don't know why the author chose num_samples_cls to 4. But I guess when batch_size = num_classes * num_samples_cls, this meets the spirit of class-balanced sampling.

from classifier-balancing.