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# CPUReg2 Example -- Source code file cpureg2.R   #
###################################################

# Read and print data frame.
cpu = read.table("cpu.txt", header=T)
cat("CPU data frame:\n")
print(cpu)

# Full regression model.
model1 <- lm(CpuTime ~ CardsIn + LinesOut + Steps + 
   MountedDevices, data=cpu)
cat("Full regression model:\n")
print(summary(model1))

# Remove least significant regressor CardsIn.
model2 <- lm(CpuTime ~ LinesOut + Steps + 
   MountedDevices, data=cpu)
cat("Regression model with CardsIn removed:\n")
print(summary(model2))

# Show model with standardized regression coefficients.
model3 = lm(scale(CpuTime) ~ scale(LinesOut) + scale(Steps) + 
   scale(MountedDevices), data=cpu)
cat("Regression model with CardsIn removed,\n")
cat("standardized coeffcients:\n")
print(summary(model3))

# Create plots.
# Attach cpu data frame so its variables are available
# with unqualified names for plotting.
attach(cpu)
p <- fitted(model2)
r <- residuals(model2)
pdf("cpureg2.pdf")
plot(p, r, main="Residual Plot 1",
           xlab="Predicted Values",
           ylab="Residuals")
abline(h=0, lty="dashed")

plot(LinesOut, r, main="Residual Plot 2",
           xlab="Number of Lines Output",
           ylab="Residuals")
abline(h=0, lty="dashed")

plot(Steps, r, main="Residual Plot 3",
           xlab="Number of Programs Loaded",
           ylab="Residuals")
abline(h=0, lty="dashed")

plot(MountedDevices, r, main="Residual Plot 4",
           xlab="Number of Mounted Devices",
           ylab="Residuals")
abline(h=0, lty="dashed")

qqnorm(r, main="Normal Plot for Residuals",
          ylab="Residuals")
dev.off( )