r-invert-polynomial

notes/index.md

@@ -9,6 +9,10 @@
 - [Linux audio recipes](/notes/linux-audio-recipes)
 - [Acoustics figures](/notes/acoustics-figures)
 
+## R
+
+- [Invert a polynomial in R](/notes/r-invert-polynomial.md)
+
 ## Mathematical visualisations
 
 - [Collatz Conjecture](/notes/collatz-conjecture)

notes/r-invert-polynomial.md

@@ -0,0 +1,23 @@
+# Inverting a polynomial using R
+
+R code to numerically find the inverse of a polynomial.
+
+```r
+# Define a polynomial function to invert
+pn <- function(x) {
+  return(3*x^3 + 2*x^2)
+}
+
+# Generic invert() function
+invert = function(fn, interval = NULL, ...){
+  Vectorize(function(y){
+    uniroot(function(x){fn(x)-y}, interval, ...)$root
+  })
+}
+
+# Inversion function specific to pn()
+pn.inverse <- invert(pn, interval = c(-10, 10))
+
+# Find the inverse for a specific value
+pn.inverse(4)
+```