message: Simplified formula for FTRL update.
diff: @@ -2114,7 +2114,8 @@ class SparseApplyFtrlOp : public OpKernel {
  accum.pow(-lr_power_scalar)) / \
  lr_scalar * var; \
  } \
  - auto x = (linear.constant(l1_scalar) * linear.sign() - linear); \
  + auto l1_reg_adjust = linear.cwiseMin(l1_scalar).cwiseMax(-l1_scalar); \
  + auto x = l1_reg_adjust - linear; \
  if (lr_power_scalar == static_cast<T>(-0.5)) { \
  auto y = new_accum.sqrt() / new_accum.constant(lr_scalar) + \
  linear.constant(static_cast<T>(2) * l2_scalar); \
  @@ -2124,8 +2125,6 @@ class SparseApplyFtrlOp : public OpKernel {
  linear.constant(static_cast<T>(2) * l2_scalar); \
  var = x / y; \
  } \
  - var = (linear.abs() > linear.constant(l1_scalar)) \
  - .select(var, var.constant(static_cast<T>(0))); \
  accum += grad_to_use.square();
  if (has_l2_shrinkage) {
  