% Curve Fit Example Problem
format compact
clc
% Data Set at 70 deg C
time1 = [0 1 3]; % x-variable
PD1 = [5.06 4.00 2.75]; % y-variable

% Curve fit polynomial fit command: polyfot(x,y,order number)
coefficients1 = polyfit(time1,PD1,1); %b=slope=coefficients1(1), a=intercept
D70=-1/coefficients1(1);

%Compare data vs model values
time_values1=linspace(0,3,100); % 100 equally spaced points from 0 to 3
PD_Model1=polyval(coefficients1, time_values1); %model calculated values

plot(time1, PD1, '*', time_values1, PD_Model1, '-k')
xlabel('Time in Minutes')
ylabel('Population density in CFU/mL')
title('Comparison of Measured and Predicted E.coli Values in Activation at 70 C')
grid on %on/off switch (off default)
box on
%-----------------------------------------------------------------------
% plotting next data set in a new figure window

figure(2)
%Data set at 60 Deg C
time2=[0 1 3 6 10 15]; %x-variable
PD2=[7.35 7.23 7.1 6.9 5.51 4.36]; %y-variable
coefficients2=polyfit(time2,PD2,1); %b=slope=coefficients2(1), a=intercept

%Compare data vs model values
time_values2=linspace(0,15,100); % 100 equally spaced points from 0 to 15
PD_Model2=polyval(coefficients2, time_values2); %model calculated values

plot(time2,PD2,'*',time_values2,PD_Model2,'-k')
xlabel('Time in Minutes')
ylabel('Population density in CFU/mL')
title('Comparison of Measured and Predicted E.coli Values in Activation at 60 C')
grid on
box on

figure(3)
%Data set at 50 Deg C
time3 = [0 1 3 6 10 15]; %x
PD3 = [7.52,7.45,7.42,7.35,7.14,6.95]; %y

coefficients3=polyfit(time3,PD3,1); %b=slope=coefficients2(1), a=intercept

%Compare data vs model values
time_values3=linspace(0,15,100); %100 equally spaced points from 0 to 15
PD_Model3=polyval(coefficients3,time_values3); %model calculated values

plot(time3,PD3,'*',time_values3,PD_Model3,'-k')
xlabel('Time in Minutes')
ylabel('Population density in CFU/mL')
title('Comparison of Measured and Predicted E.coli Values in Activation at 50 C')
grid on
box on