Add demo of formatted math in Roxygen header with LaTeX

NAMESPACE

@@ -1,3 +1,4 @@
 # Generated by roxygen2: do not edit by hand
 
 export(example_function)
+export(math_demo)

R/math_demo.R

@@ -0,0 +1,83 @@
+#' Demonstrate LaTeX Math Formatting in Roxygen
+#'
+#' This function demonstrates how to include formatted mathematical expressions
+#' in roxygen2 documentation using LaTeX syntax.
+#'
+#' @description
+#' The quadratic formula is given by:
+#' \deqn{x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}}{
+#'   x = (-b ± sqrt(b^2 - 4ac)) / (2a)}
+#'
+#' For inline math, the variance is denoted \eqn{\sigma^2}{sigma^2},
+#' and the standard deviation is \eqn{\sigma}{sigma}.
+#'
+#' @details
+#' This function computes the roots of a quadratic equation of the form:
+#' \deqn{ax^2 + bx + c = 0}{ax^2 + bx + c = 0}
+#'
+#' The discriminant is \eqn{\Delta = b^2 - 4ac}{Delta = b^2 - 4ac}.
+#' When \eqn{\Delta > 0}{Delta > 0}, there are two real roots.
+#' When \eqn{\Delta = 0}{Delta = 0}, there is one repeated real root.
+#' When \eqn{\Delta < 0}{Delta < 0}, there are two complex conjugate roots.
+#'
+#' Additional mathematical notation examples:
+#' \itemize{
+#'   \item Sum notation: \eqn{\sum_{i=1}^{n} x_i}{sum(x_i, i=1..n)}
+#'   \item Integral: \eqn{\int_{0}^{\infty} e^{-x} dx = 1}{
+#'     integral from 0 to infinity of e^(-x) dx = 1}
+#'   \item Matrix multiplication:
+#'     \eqn{\mathbf{Y} = \mathbf{X}\boldsymbol{\beta} +
+#'     \boldsymbol{\epsilon}}{Y = X*beta + epsilon}
+#'   \item Greek letters: \eqn{\alpha, \beta, \gamma, \delta}{
+#'     alpha, beta, gamma, delta}
+#' }
+#'
+#' @param a Numeric coefficient of \eqn{x^2}{x^2}
+#' @param b Numeric coefficient of \eqn{x}{x}
+#' @param c Numeric constant term
+#'
+#' @return A numeric vector of length 1 or 2 containing the root(s) of
+#'   the equation. Complex roots are returned as complex numbers.
+#'
+#' @export
+#'
+#' @examples
+#' # Two real roots: x^2 - 5x + 6 = 0
+#' # Solution: x = 2 or x = 3
+#' math_demo(1, -5, 6)
+#'
+#' # One repeated root: x^2 - 4x + 4 = 0
+#' # Solution: x = 2
+#' math_demo(1, -4, 4)
+#'
+#' # Complex roots: x^2 + 2x + 5 = 0
+#' # Solution: x = -1 ± 2i
+#' math_demo(1, 2, 5)
+math_demo <- function(a, b, c) {
+  # Check for valid input
+  if (isTRUE(all.equal(a, 0))) {
+    stop("Coefficient 'a' must be non-zero for a quadratic equation")
+  }
+
+  # Calculate discriminant
+  discriminant <- b^2 - 4 * a * c
+
+  # Calculate roots based on discriminant
+  if (discriminant > 0) {
+    # Two distinct real roots
+    root1 <- (-b + sqrt(discriminant)) / (2 * a)
+    root2 <- (-b - sqrt(discriminant)) / (2 * a)
+    return(c(root1, root2))
+  } else if (discriminant == 0) {
+    # One repeated real root
+    root <- -b / (2 * a)
+    return(root)
+  } else {
+    # Two complex conjugate roots
+    real_part <- -b / (2 * a)
+    imaginary_part <- sqrt(-discriminant) / (2 * a)
+    root1 <- complex(real = real_part, imaginary = imaginary_part)
+    root2 <- complex(real = real_part, imaginary = -imaginary_part)
+    return(c(root1, root2))
+  }
+}

inst/WORDLIST

@@ -4,6 +4,7 @@ CodeFactor
 Codecov
 DOCX
 Lifecycle
+Roxygen
 MathJax
 RevealJS
 Shortcode
@@ -15,6 +16,7 @@ callout
 callouts
 cdot
 emplate
+roxygen
 foldable
 frac
 frontmatter

tests/testthat/test-math_demo.R

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+test_that("math_demo handles two distinct real roots", {
+  # x^2 - 5x + 6 = 0 has roots x = 2 and x = 3
+  result <- math_demo(1, -5, 6)
+  expect_length(result, 2)
+  expect_type(result, "double")
+  expect_equal(sort(result), c(2, 3))
+})
+
+test_that("math_demo handles one repeated real root", {
+  # x^2 - 4x + 4 = 0 has root x = 2 (repeated)
+  result <- math_demo(1, -4, 4)
+  expect_length(result, 1)
+  expect_type(result, "double")
+  expect_equal(result, 2)
+})
+
+test_that("math_demo handles complex roots", {
+  # x^2 + 2x + 5 = 0 has complex roots x = -1 ± 2i
+  result <- math_demo(1, 2, 5)
+  expect_length(result, 2)
+  expect_type(result, "complex")
+  expect_equal(Re(result[1]), -1)
+  expect_equal(Re(result[2]), -1)
+  expect_equal(abs(Im(result[1])), 2)
+  expect_equal(abs(Im(result[2])), 2)
+})
+
+test_that("math_demo throws error when a = 0", {
+  expect_error(
+    math_demo(0, 5, 3),
+    "Coefficient 'a' must be non-zero for a quadratic equation"
+  )
+})
+
+test_that("math_demo works with different coefficients", {
+  # 2x^2 - 8x + 6 = 0 has roots x = 1 and x = 3
+  result <- math_demo(2, -8, 6)
+  expect_length(result, 2)
+  expect_equal(sort(result), c(1, 3))
+})