Return the max, min, and zeros of a function y, and plot it, R

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#R version 3.3.2
# Return the max, min, and zeros of a function y, and plot same.
library(ggplot2)
pi=3.1416
b=(2*pi)/365.2422
c=-79.5*b
d=seq(0,365,1)
y=23.44*sin((b*d)+c)
cat("The max. of y is", max(y), "and occurs at index", which.max(y), "\n")
cat("The min. of y is", min(y), "and occurs at index", which.min(y), "\n")
# Search the function output vector y for zeros and return exact zero(s), or a pair of 
#   adjacent values between which a zero exists.
cat("Searching for the zero points in vector y...\n")
for(i in 2:length(y)) { 
  test=abs(sign(y[i-1])+sign(y[i]));
  if(test==0) { cat("x.indexes",i-1,i,"y.values",y[i-1],y[i],"\n") };
  if(test==1 && y[i]==0) { cat("x.index",i,"y.value",y[i],"\n") }; 
}
# Now plot the function
title1="Approximate Solar Declination by Day of Year"
qplot(d,y,geom="path",main=title1,xlab="Day of Year",ylab="Solar Declination")+
scale_x_continuous(breaks=seq(0,365,73))+scale_y_continuous(breaks=seq(-25,25,5))+
geom_line(aes(x=80.5,y=y),color="green")+geom_line(aes(x=263,y=y),color="orange")+
geom_line(aes(x=172,y=y),color="yellow")+geom_line(aes(x=354,y=y),color="blue")+
annotate("text",x=c(36,126,217,308),y=-5,label=c("Winter","Spring","Summer","Fall"))

[ + ] Show input
Absolute running time: 1.41 sec, cpu time: 1.76 sec, memory peak: 50 Mb, absolute service time: 1,43 sec