function sawtooth(data, width, height, opts = {}) {
let nb_parts = 10
const x = d3.scaleTime()
.domain([new Date("2020-01-01"), new Date("2020-05-01")])
.range([0, width])
const node = DOM.svg(400, 300)
const svg = d3.select(node)
svg.attr('style', 'border: 1px solid gray');
return svg.node();
}