data_str = '54 74 62 85 55 88 85 51 85 54 84 78 47 83 52 62 84 52 79 51 47 78
69 74 83 55 76 78 79 73 77 66 80 74 52 48 80 59 90 80 58 84 58 73
83 64 53 82 59 75 90 54 80 54 83 71 64 77 81 59 84 48 82 60 92 78
78 65 73 82 56 79 71 62 76 60 78 76 83 75 82 70 65 73 88 76 80 48
86 60 90 50 78 63 72 84 75 51 82 62 88 49 83 81 47 84 52 86 81 75
59 89 79 59 81 50 85 59 87 53 69 77 56 88 81 45 82 55 90 45 83 56
89 46 82 51 86 53 79 81 60 82 77 76 59 80 49 96 53 77 77 65 81 71 70
81 93 53 89 45 86 58 78 66 76 63 88 52 93 49 57 77 68 81 81 73 50 85
74 55 77 83 83 51 78 84 46 83 55 81 57 76 84 77 81 87 77 51 78 60 82
91 53 78 46 77 84 49 83 71 80 49 75 64 76 53 94 55 76 50 82 54 75 78
79 78 78 70 79 70 54 86 50 90 54 54 77 79 64 75 47 86 63 85 82 57 82
67 74 54 83 73 73 88 80 71 83 56 79 78 84 58 83 43 60 75 81 46 90 46 74'

ss = strsplit( data_str, "[ \n]", perl=TRUE )
data = as.vector( sapply( ss, as.double ) )

# Part (a):
#
#postscript("../../WriteUp/Graphics/Chapter10/ex_4_density.eps", onefile=FALSE, horizontal=FALSE)
plot( density( data, adjust=1.0 ), main='time between Old Faithful eruptions' ) 
grid()
#dev.off()

# Part (b):
#
n = length(data)
x = data[1:(n-1)]
y = data[2:n]
m = lm( y ~ x )
#postscript("../../WriteUp/Graphics/Chapter10/ex_4_time_1_vs_time_2.eps", onefile=FALSE, horizontal=FALSE)
plot( x, y, xlab='time from last eruption (minutes)', ylab='time to next eruption (minutes)' )
abline(m, col='red')
grid()
#dev.off()