ImportError: cannot import name 'exponential_decay'

This error typically occurs when you try to import a function called `exponential_decay` from a module or package, but that function is not defined in that module or package.

To fix this error, you can check if you have misspelled the function name or if the function is actually defined in the module or package you are trying to import it from.

If the function is not defined, you can either define it yourself or import it from another module that has the function definition.