Linear Regression example doesn't work.
create_op: NoOp 'GradientDescent', inputs: empty, control_inputs: GradientDescent/update_weight/ApplyGradientDescent, GradientDescent/update_bias/ApplyGradientDescent, outputs: empty
create_op: NoOp 'init', inputs: empty, control_inputs: weight/Assign, bias/Assign, outputs: empty
Epoch: 50 cost=NaN W=NaN b=NaN
Epoch: 100 cost=NaN W=NaN b=NaN