Free Course on Response Surface Methodology with R
R Code for Lesson 3: Analyzing a 22 Design with Central Points
Copy and paste the code below in your R Studio to follow the example in Lesson 3: Analyzing a 22 Design – R tutorial
# Analysis for a 2^2 Design with Central Points
# Author: Rosane Rech, January 2021.
# This code is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
# https://creativecommons.org/licenses/by-nc-sa/4.0/
# Data source:
# Design and analysis of experiments / Douglas C. Montgomery. — Eighth edition.
# ISBN 978-1-118-14692-7
# Data file: DoEOpt04.csv
# Time (x1): Time (min)
# Temp (x2): Temperature (ºC)
# Y: Yield (%)
# building the data set
# (run this code to build the DoEOpt04 data set before following the analysis)
<- data.frame(x1 = c(-1,-1,1,1,0,0,0,0,0),
DoEOpt04 x2 = c(-1,1,-1,1,0,0,0,0,0),
Time = c(30,30,40,40,35,35,35,35,35),
Temp = c(150,160,150,160,155,155,155,155,155),
Y = c(39.3,40,40.9,41.5,40.3,40.5,40.7,40.2,40.6)
)
# loading Response Surface Methodology package
library(rsm)
# file view
str(DoEOpt04)
# setting the relationship between coded and natural variables
<- as.coded.data(DoEOpt04,
DoEOpt04 ~ (Time-35)/5,
x1 ~ (Temp-155)/5)
x2
# regression model with coded variables
<- rsm(Y ~ FO(x1,x2) + TWI(x1,x2), data = DoEOpt04)
model summary(model)
# contour plot
contour(model, ~ x1+x2,
image = TRUE,
xlabs=c("Time (min)", "Temperature (ºC)"))
points(DoEOpt04$Time,DoEOpt04$Temp)