I would like to show a nice cross-reference to a picture in the HTML document I'm creating with R Markdown. However, even if I followed the bookdown section on cross-references, I cannot get the reference to show in the final HTML output. I'm working in R Studio, if that helps. .Rmd file:
---
title: "ppp"
author: "ppp"
date: "July 4, 2017"
output:
html_document:
fig_caption: yes
---
```{r setup, include=FALSE}
library(knitr)
opts_chunk$set(echo = FALSE)
```
```{r foo, fig.cap="$f_{p}$ as a function of $g$ for various values of $r=\\frac{\\rho_{w}}{\\rho_{a}}$"}
# All defaults
include_graphics("download.jpg")
```
A cross-reference to figure \@ref(fig:foo).
The output I get is
So the caption is rendering correctly, but the cross-reference is not being created. How do I fix that?