force力向导图布局节点间距离受什么因素影响？echarts graph配置项内容和展示

节点间的距离受什么因素影响？，可以怎么设置改变节点之间的距离？

      var uploadedDataURL = "/asset/get/s/data-1499235712572-BkKKrbcNZ.gexf";


myChart.showLoading();

$.get(uploadedDataURL, function(xml) {
    console.log(1111);
    myChart.hideLoading();

    var graph = echarts.dataTool.gexf.parse(xml);
    var categories = [];
    for (var i = 0; i < 9; i++) {
        categories[i] = {
            name: '类目' + i
        };
    }
    // console.log(graph.links);
    graph.nodes.forEach(function(node) {
        node.itemStyle = null;
        node.value = node.symbolSize;
        // node.symbolSize /= 1.5;
        node.label = {
            normal: {
                show: node.symbolSize > 0,
                // textStyle:{
                //     fontSize:node.symbolSize>30?node.symbolSize/3:(node.symbolSize>10?node.symbolSize/2:node.symbolSize*2)
                // }
            }
        };
        node.category = node.attributes.modularity_class;
        node.draggable = true;
    });
    option = {
        //color:
        title: {
            text: 'test',
            subtext: 'Default layout',
            top: 'bottom',
            left: 'left'
        },
        tooltip: {},
        legend: [{
            // selectedMode: 'single',
            data: categories.map(function(a) {
                return a.name;
            })
        }],
        animationDuration: 1500,
        animationEasingUpdate: 'quinticInOut',
        series: [{
            name: 'test',
            type: 'graph',
            layout: 'force',
            data: graph.nodes,
            links: graph.links,
            categories: categories,
            focusNodeAdjacency: true,
            roam: true,
            label: {
                normal: {
                    position: 'right',
                    formatter: '{b}'
                }
            },
            lineStyle: {
                normal: {
                    color: 'source',
                    curveness: 0.3
                }
            },
            force: {
                repulsion: 650,
                gravity: 0.25,
                edgeLength: [100, 150]
            }
        }]
    };

    myChart.setOption(option);
}, 'xml');