Estimated LOS velocities of simulated galaxy clusters in the Magneticum simulations with our machine-learning approach compared to the true values. X-axis: true LOS velocities of simulated galaxy clusters in the Magneticum simulations. Y-axis: estimated LOS velocities of the same galaxy clusters with our machine-learning approach in Sect. 3.1 when the RSD effect is not included (left) and included (right). The projected distributions along the X-axis and Y-axis are shown on the top and right panels. In addition, the result of the linear fit is shown between the true and estimated LOS velocities as the red dashed line, which is compared to the case where they are equal, which is shown by the blue dashed line.