JuliaPlots/Plots.jl

[FR] Allow plotting function data in quiver()

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#4,890 opened on Feb 19, 2024

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enhancementgood first issue

Description

The easiest mathematical way to define a 2D vector field is as a function with two arguments that outputs a 2 item vector

julia> vecField(x,y) = [x^2, y+1x]

Unfortunately, quiver can't plot this

julia> quiver(vecField)  
ERROR: vecField is not a Function, or is not defined at any of the values [-5.0, -1.0, 0.0, 0.01]

It'd be pretty neat if we could add some recipie that evaluates a 2d function given to quiver at reasonable points, making plotting a vector field into a nice, neat one-liner, instead of the current solution which is somewhat more involved. Such a recipe would also probably want to apply scaling to arrows, perhaps by dividing all outputs by the norm of the largest output.

Contributor guide

Tech stack
None
Domain
api
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
None
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Examine the existing `quiver` function implementation in Plots.jl, likely in `src/recipes.jl`. Understand how it currently handles arrays and how other recipes accept functions (e.g., `plot(f)`). Add a new method that takes a function `f(x,y)` returning a 2 element vector, evaluates it over a grid defined by `xlims` and `ylims`, and then calls the existing quiver with the computed arrays. Consider scaling arrows by dividing by the maximum norm. Check issue comments for any additional context or constraints.