#*****************************************************************************80
#
## caffeine_scatter: scatter plot of cataract incidence / caffeine intake.
#
#  Licensing:
#
#    This code is distributed under the MIT license. 
#
#  Modified:
#
#    25 August 2020
#
#  Author:
#
#    John Burkardt
#
cat ( date ( ), "\n" )
cat ( "\n" )
cat ( "caffeine_scatter\n" )
cat ( " ", version$version.string, "\n" )
cat ( "  Read a data file of cataract incidence versus caffeine intake." )
cat ( "  Display the data as a scatter plot.." )

filename = "caffeine_data.txt"
data <- read.table ( filename, header = FALSE )

cataracts = data[,1]
caffeine = data[,2]
#
#  Get least squares line
#
lm ( caffeine ~ cataracts )

filename = "caffeine_scatter.png"

png ( filename )
plot ( data[,1], data[,2], 
  xlab = "Daily caffeine intake (mg)", 
  ylab = "Blindness due to cataracts (%)",
  main = "Caffeine and cataracts",
  pch = 19,
  col = "red" )
#
#  Draw least squares line.
#  I haven't figured out how to extract these values from lm().
#
abline ( 212.650, -4.031 )

grid ( )
cat ( '  Graphics saved as "', filename, '"\n' )
#
#  Terminate.
#
cat ( "\n" )
cat ( "caffeine_scatter:\n" )
cat ( "  Normal end of execution.\n" )

quit ( )