function getViewRect$4(seriesModel, api) {
    return getLayoutRect(
        seriesModel.getBoxLayoutParams(), {
            width: api.getWidth(),
            height: api.getHeight()
        }
    );
}
Using Gauss-Seidel iterations method to compute the node depth(y-position)

@param {module:echarts/data/Graph~Node} nodes  node of sankey view
@param {module:echarts/data/Graph~Edge} edges  edge of sankey view
@param {number} height  the whole height of the area to draw the view
@param {number} nodeGap  the vertical distance between two nodes
    in the same column.
@param {number} iterations  the number of iterations for the algorithm