I have a graph with nodes and edges and I want to display them. Isn't there any function which, given this graph, displays it without me to give exact coordinates?
yes, you can use the auto layout http://jgraph.github.io/mxgraph/docs/js-api/files/layout/mxCompactTreeLayout-js.html this url construct a compact tree layout.
var layoutMgr = new mxLayoutManager(graph);
layoutMgr.getLayout = function(cell) {
return layout;
};