To add the trendline quation to the plot, see last two lines of the code below.
avgspeed = [27.78; 31.14; 33.36; 37.07; 38.50; 41.38]; %the x values
height = [13; 33; 55; 155; 245; 519]; %the raw y values
%next: make a matrix with a column of ones and a column of the x values
X=[ones(length(avgspeed),1) avgspeed]; %X=(column of ones,column of x values)
Y=log10(height); %log(height), for the regression
%next line: the standard matrix equation for a linear regression
b=inv(X'*X)*X'*Y; %b(1)=intercept, b(2)=slope
predheight=10.^(X*b); %the heights predicted by the linear regresison
semilogy(avgspeed,height,'rx',avgspeed,predheight,'r-');
xlabel('Avg.Speed'); ylabel('Height');
textstr=sprintf('Pred.Height=\n10^{(%.3f+%.3f*AvgSpeed)}',b(1),b(2));
text(27,520,textstr);
The code above produces the plot below.
