function breakeven(C,S,F)
% function breakeven(C,S,F)
% this function will prepare a break even chart with linear cost and
% sales income lines.   
% S. Scott Moor                      March 2008
%
% Inputs:   C = Variable Cost ($/unit)
%           S = Sales Price ($/unit)
%           F = Fixed cost (million $)
% Output:   A Break even graph with axes in millions of units and millions
%           of dollars.  

% Internal Variables:
%   xBE = vnit volume for breakeven point (millions of units)
%   x = vector of unit volumes from zero to two times the break even volume
%   Cost = vector of total cost for the unit volumes in x 
%   Sales = vector of sales inclome the for unit volumes in x
%   BE = text variable of unit volume for breakeven point (millions of units)
%   Ft, Ct, St = text variables for graph title containing the input values
%   

% Solve for break even point 
xBE = F./(S - C);

% Prepare x vector (millions of units produced)
x = linspace(0,2*xBE,50);
% Prepare the cost vector
Cost = F + C.*x;
% Pepare sales income vector 
Sales = S.*x;
% set up fixed cost vectors
x1 = [0, 2*xBE]; y = [F, F];

% Plot breakeven chart with a marker at the breakeven even point and label the plot
plot(x,Cost,x,Sales,'--',x1,y,':', xBE, xBE*S,'p','MarkerSize',12)
xlabel('Production Quantity (million units)');
ylabel('Production Cost or Sales Income(million $)')
% Convert breakeven point to a string variable and use in graph legend 
BE = num2str(xBE);
legend('Total Production Cost','Total Sales Income', 'Fixed Costs', ...
         ['Breakeven Point = ' BE,' million units'], 'Location','NorthWest')
% Convert input values to strings and form a graph title that displays the inputs 
Ft = ['Fixed Costs = ', num2str(F),' million $,  '];
St = ['Sales Price = ', num2str(S), ' $/unit,  '];
Ct = ['Variable Cost = ', num2str(C), ' $/unit'];      
title(['Breakeven Chart: ',Ft,St,Ct])