keras/src/optimizers/adagrad.py/Adagrad/build
class Adagrad:    def build(self, var_list):
        if self.built:
            return
        super().build(var_list)
        self._accumulators = []
        initializer = initializers.Constant(self.initial_accumulator_value)
        for var in var_list:
            self._accumulators.append(
                self.add_variable(
                    shape=var.shape,
                    initializer=initializer,
                    dtype=var.dtype,
                    name="accumulator",
                )
            )