keras/src/optimizers/base_optimizer.py/BaseOptimizer/assign_sub
class BaseOptimizer:    def assign_sub(self, variable, value):
        """Subtract a value from a variable.

        This should be used in optimizers instead of
        `variable.assign_sub(value)` to support backend specific optimizations.
        Note that the variable can be a model variable or an optimizer variable;
        it can be a backend native variable or a Keras variable.

        Args:
            variable: The variable to update.
            value: The value to add to the variable.
        """
        variable.assign_sub(value)