Rmarkdown inline latex error - knitr

Question

I have an R function that returns text, including some LaTeX math mode, and I'm trying to use this text from an inline r chunk in an rmarkdown document. However, I get some quite strange behaviour regarding the use of math mode that I don't understand. It may be related to this question.
The following example works:
---
title: "Untitled"
output: pdf_document
---
```{r print_function}
print_fun <- function(x){
return(paste0("$\\mathrm{p}(\\beta < 0)$ > ", x))
}
x <- 0.5
```
Testing our printing function, we get `r print_fun(x)`.
Producing output
A small change breaks it
If I move the $ symbol a few places to the right, in order to also include the > sign within the math mode block, the document no longer compiles:
```{r print_function}
print_fun <- function(x){
return(paste0("$\\mathrm{p}(\\beta < 0) > $", x))
}
x <- 0.5
```
With the following error message:
Error producing PDF.
! LaTeX Error: \mathrm allowed only in math mode.
See the LaTeX manual or LaTeX Companion for explanation.
Type H <return> for immediate help.
...
l.137 ...g our printing function, we get \$\mathrm
Error: pandoc document conversion failed with error 43
Execution halted
This code works in an RSweave document, and I don't see why including the > symbol into math mode would have this effect.
Closing math mode after the numerical reference compiles again
```{r print_function}
print_fun <- function(x){
return(paste0("$\\mathrm{p}(\\beta < 0) > ", x, "$"))
}
x <- 0.5
```
Why?

Answer 1

This problem is to do with the space before the $ symbol in maths mode. From trial and error, this happens when the expression contains any maths function such as \\mathrm{}. So as minimal examples:
Works:
---
output: pdf_document
---
`r paste0("$\\mathrm{p}$")`
$\mathrm{p}$
Doesn't work:
---
title: "Untitled"
output: pdf_document
---
`r paste0("$\\mathrm{p} $")`
$\mathrm{p} $
Solution:
In your case, you are best off pasting the $ symbol after the value of the function:
print_fun <- function(x){
return(paste0("$\\mathrm{p}(\\beta < 0) >", x, "$"))
}
This lets you have the space after the > symbol.