Playground
Place black and white dots, then watch chapter 4's network learn to tell them apart, one batch at a time.
The playground runs in your browser and needs JavaScript.
Arrow keys move a cursor, with Shift for longer moves. Space uses the brush, Delete erases the dot under the cursor, B, W and E pick black, white or erase, Enter selects the dot under the cursor and Escape clears the selection.
step 0 · epoch 0loss 0.725 · 38 of 200 right
Point at the field or select a dot to see the network compute.Tap a dot to see the network compute.
What you're seeing
The color under the dots is the network's answer for every point of the plane: how sure it is that a dot there would be white. The ink line is where it can't decide, at p = 0.5. A dot it gets wrong carries a second ring.
Each step takes a batch of dots, measures how wrong the network is on them, runs that error backward to get a gradient for every weight, and moves each weight a small step against it. Step slows one of those down, with the rest of the dots faded.
Change the dots while it trains and the loss jumps, because the question changed. Faint ticks on the loss curve mark those edits.