code: def ystep(self):
          
  
          # Extract AMS part of ystep argument so that it is not
          # affected by the main part of the ystep
          amidx = self.index_addmsk()
          Yi = self.cbpdn.AX[amidx] + self.cbpdn.U[amidx]
          # Perform main part of ystep from inner cbpdn object
          self.inner_ystep()
          # Apply mask to AMS component and insert into Y from inner
          # cbpdn object
          Yi[np.where(self.W.astype(np.bool))] = 0.0
          self.cbpdn.Y[amidx] = Yi
docs: This method is inserted into the inner cbpdn object,
          replacing its own ystep method, thereby providing a hook for
          applying the additional steps necessary for the AMS method.