Quiver — A Two-Dimensional Vector Field

Mix.install([
  {:plotly_ex, "~> 0.3"},
  {:kino, "~> 0.18"}
])

Positions and vector components

Quiver arrows start at (x, y) and carry horizontal/vertical components (u, v). Here the field rotates around the origin. lengthmode: "raw" keeps vector lengths in data units; lengthfactor scales them for readability. Equal axis scales preserve the apparent direction. The title also demonstrates MathJax 4.

alias Plotly.{Figure, Quiver}

positions = for x <- -2..2, y <- -2..2, do: {x, y}

Figure.new()
|> Figure.add_trace(Quiver.new(
  x: Enum.map(positions, &elem(&1, 0)),
  y: Enum.map(positions, &elem(&1, 1)),
  u: Enum.map(positions, fn {_x, y} -> -y end),
  v: Enum.map(positions, fn {x, _y} -> x end),
  lengthmode: "raw", lengthfactor: 0.3, anchor: "tail",
  marker: %{color: "steelblue"}
))
|> Figure.update_layout(
  title: %{text: "$\\vec{F}(x,y)=(-y,x)$"},
  xaxis: %{range: [-3, 3]}, yaxis: %{range: [-3, 3], scaleanchor: "x"}
)
|> Plotly.show()