Cross-entropy usually consumes probabilities produced by softmax. This book keeps softmax named and starts from a displayed exact probability vector.

highlighted = computed this step

Probabilities come from softmax

In the attention and decoding books, softmax was already the named boundary that turns logits into probabilities. Cross-entropy starts after that boundary: it consumes a pinned probability distribution and applies a named log to the selected entry.

softmax namedplog(pk) named\text{softmax named}\rightarrow p\rightarrow -\log(p_k)\text{ named}
Cross-entropy exactlyOne-hot selection with named log boundary.cross-entropy term selectionclassy_ip_itermA01/40 (one-hot drop)B11/2-log(1/2)C01/40 (one-hot drop)H=-log(1/2)exact one-hot selection plus named log boundary; one loss on one pinned probabilitydistribution; NOT learning

The log-loss link

The logistic scoring book used the same structure: choose the class term, then name the logarithm instead of pinning a decimal. Cross-entropy is the multi-class version of that same honesty split.

selected probabilitynamed log loss\text{selected probability}\rightarrow\text{named log loss}
Cross-entropy exactlyOne-hot selection with named log boundary.cross-entropy term selectionclassy_ip_itermA01/40 (one-hot drop)B11/2-log(1/2)C01/40 (one-hot drop)H=-log(1/2)exact one-hot selection plus named log boundary; one loss on one pinned probabilitydistribution; NOT learning

Summary

This book does not compute softmax as exact. It assumes the probability vector is the displayed exact input, then names the logarithm where the next boundary appears.

probabilities displayed; log named\text{probabilities displayed; log named}
Cross-entropy exactlyOne-hot selection with named log boundary.cross-entropy term selectionclassy_ip_itermA01/40 (one-hot drop)B11/2-log(1/2)C01/40 (one-hot drop)H=-log(1/2)exact one-hot selection plus named log boundary; one loss on one pinned probabilitydistribution; NOT learning