There's are a couple of misquotes there. For starters, it's not "w1 ← w1 − η ∂w|∂L" but "w1 ← w1 − η ∂L|∂w1". Also, the second "if" should say "negative", not "

There's are a couple of misquotes there. For starters, it's not "w1 ← w1 − η ∂w|∂L" but "w1 ← w1 − η ∂L|∂w1". Also, the second "if" should say "negative", not "positive" again. In case you were being sarcastic, it is simple if you don't take it out of context. It requires a certain understanding of derivatives, but a reader who doesn't understand them won't make it to the point you're quoting.