var startX = 100;
var startY = 100;
var curve = 211.4;
var amplitude = 5;
var targetX = 200;
var targetY = 200;

var svg = d3.select("svg")
svg.append("path")
  .attr('stroke','blue')
  .attr('stroke-width',3)
  .attr('fill','black')
  .attr('d','M '+startX+' '+startY+' q '
        +curve+' '+amplitude+' '
        +targetX+' '+targetY+''
        +'l'+0+' '+(-targetY) + 'Z'
//        +'l'+(-targetX)+' '+0)
       )