Partial Eltwise Layer in Caffe

[Xinyu Pan]

Hi,

I want to implement a partial eltwise layer as follows:

Bottom_0: N * C * X * Y

Bottom_1: N * C * 1

Top_0: N * C * X * Y

Top_0[n][c][x][y] = Bottom_1[n][c][1] * Bottom_0[n][c][x][y]

I wonder if this can be built by using other basic layers in some efficient way. I also found that scale_layer is very similar to this. 

Thank you very much.

[Przemek D]

I would use TileLayer to "upscale" Bottom_1 so it matched the exact size of Bottom_0 and then perform Eltwise with PROD operation. Since TileLayer only works in one axis at a time, you'll need to do it like this:

layer {
  name: "tile_x"
  type: "Tile"
  bottom: "Bottom_1"
  top: "Bottom_1_tiled_x"
  tile_param {
    axis: 2
    tiles: <X>
  }
}
layer {
  name: "tile_y"
  type: "Tile"
  bottom: "Bottom_1_tiled_x"
  top: "Bottom_1_tiled"
  tile_param {
    axis: 3
    tiles: <Y>
  }
}

<X> and <Y> should refer to your numbers in Bottom_0 blob. After those operations, your Bottom_1_tiled can be element-wise multiplied with Bottom_0.

PS: I just noticed your Bottom_1 is 3D instead of 4D - is this correct? In this case you might want to use ReshapeLayer to add another dimension in which you'll tile.