keras/src/optimizers/ftrl.py/Ftrl/build
class Ftrl:    def build(self, var_list):
        """Initialize optimizer variables.

        Args:
            var_list: list of model variables to build Ftrl variables on.
        """
        if self.built:
            return
        super().build(var_list)
        self._accumulators = []
        self._linears = []
        for var in var_list:
            self._accumulators.append(
                self.add_variable(
                    shape=var.shape,
                    dtype=var.dtype,
                    name="accumulator",
                    initializer=initializers.Constant(
                        self.initial_accumulator_value,
                    ),
                )
            )
            self._linears.append(
                self.add_variable_from_reference(
                    reference_variable=var, name="linear"
                )
            )