The notebook states:

The error is

`๐
+๐พmax ๐ฬ(๐ โฒ,๐โฒ;๐คโ)โ๐(๐ ,๐;๐ค)`

Which I couldnโt make sense of. Then later in the notebook the algorithm image has the above (with Q-hat) squared which makes sense since the sign of the difference shouldnโt matter. And the programming instructions refer to mean squared error.