MATLAB: Linear Regression Matlab code

codeconfusedlinear regression

Hello, this is my matlab script that is supposed to take data from an excel spread sheet and use it to create a y = mx+b function by linear regression. Here is my code and attached is the excel spread sheet. The first row is the amount in gallons and the next two rows are the amount of time it took to move the gallons in seconds.
points = xlsread('data.xlsx');
n = size(points,1);
sum_x = 0;
sum_y = 0;
sum_xy = 0;
sum_x2 = 0;
for i = i:n
    sum_x = sum_x + points(i,2);
    sum_y = sum_y + points(i,3);
    sum_xy = sum_xy + points(i,2)*(points(i,3));
    sum_x2 = sum_x2 + (points(i,2)^2);
end
a1 = (n*sum_xy – sum_x*sum_y)/(n*sum_x2 – sum_x2);
a0 = (sum_y/n)-a_1*(sum_x/n);
y_new = a1*x + a_0;
THank you for your help.

Best Answer

% First COLUMN is galon, the next two columns are amount of time required
% to remove that amount of gallons. I assumed you have two sets of
% measurements that's why there are two columns.
data=[ 0.50  66  70; ...
       0.75 100  95; ...
       1.00 129 135; ...
       1.25 161 159; ...
       1.50 198 190; ...
       1.75 230 232; ...
       2.00 265 250];
% Fitting a a polynomial t=a1*g+a0; g: Gallon, t: time
g=[data(:,1);data(:,1)];
tMeasured=[data(:,2);data(:,3)];
a=polyfit(g, tMeasured,1);
% Plot1
gModel=min(g):0.01:max(g);
tModelled=polyval(a,gModel);
figure
plot(gModel,tModelled,'r-','LineWidth',2);
hold on
plot(g,tMeasured,'kx','MarkerSize',10)
legend('Fitted Line','Measured','Location','NorthWest');
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