#*****************************************************************************80
#
## drug_dosage_plots models the variation in blood levels of a medicinal drug.
#
#  Discussion:
#
#    Drug levels in the blood, for certain drugs, can be modeled by a pair of
#    coupled first-order linear differential equations.
#
#    The concentration level must reach 800 mg / liter to be medicinally
#    effective but becomes toxic at 1000 mg / liter.
#
#    It is desired to plot the concentration level, as well as two horizontal
#    lines representing the medicinal and toxic levels.
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    23 August 2020
#
#  Author:
#
#    John Burkardt
#
#  Reference:
#
#    Soraya Dhillon, Andrzej Kostrzewski,
#    Clinical Pharmacokinetics,
#    Pharamceutical Press, 2006,
#    ISBN: 978-0-85369-571-4.
#
cat ( "\n" )
cat ( "drug_dosage_plots:\n" )
cat ( " ", version$version.string, "\n" )
cat ( "  Plot the variation over time of the concentration\n" );
cat ( "  of a medicinal drug in the bloodstream.\n" );

filename = "drug_dosage_data.txt"
data <- read.table ( filename, header = FALSE )
times = data[,1]
cc = data[,2]
n = dim(data)[1]
#
#  Plot the data.
#
filename = "drug_dosage_plots.png"
png ( filename )

plot ( times, cc,
  xlab = "<--- Time --->",
  ylab = "<--- Plasma concentration --->",
  main = "Drug level variation over time",
  col = "blue",
  type = 'l',
  lwd = 4,
  ylim = c ( 0, 1100 ) )

t2 = c ( times[1], times[n] )
m2 = c ( 800, 800 )
lines ( t2, m2, type = 'l', col = "green", lwd = 4 )

t3 = c ( times[1], times[n] )
m3 = c ( 1000, 1000 )
lines ( t3, m3, type = 'l', col = "red", lwd = 4 )

x = 5.0
y = 200.0
legend ( x, y, legend = c ( 'blue: Plasma Concentration',  'green: Medicinal Level', 'red: Toxic Level' ) )

grid ( )

cat ( "\n" )
cat ( "  Graphics saved as '", filename, "'\n" )
#
#  Terminate.
#
cat ( "\n" )
cat ( "drug_dosage_plots\n" )
cat ( "  Normal end of execution.\n" )
quit ( )