Line of Best Fit

Trying to get a line of best fit through my points.

Here is an example of my scatter plot:

x = [1 2 3 4]
z = [rate1 rate2 rate3 rate4]
scatter(x, z)

Below is what I am trying for the line of best fit but am getting an error:

fit = polyfit(x, y, 1);
fittedX = linspace(min(x), max(x), 100);
fittedZ = polyval(fit, fittedX);
hold on;
plot(fittedX, fittedZ, 'r-', 'LineWidth', 3);

[John D'Errico]

You are getting an error, but what error. How can we guess? We don't even know what y is here. You plot a scatter plot z versus x, but then fit y as a function of x. Where did y come from?

[dpb]

fittedX = linspace(min(x), max(x), 100);
fittedZ = polyval(fit, fittedX);

NB: It takes only the two points to define the line to plot between [min(x) max(x)]; the other 98 are superfluous above.

[Richard Brown]

Assuming you mean z instead of y, this code should work, assuming rate1, rate2, etc are scalars.

Answer 1

[Image Analyst]

Do you have an extra y floating around? Maybe try

clear all;

to get rid of it. You're calling

fit = polyfit(x, y, 1);

instead of

fit = polyfit(x, z, 1);

If it even works, it's because there is a y variable hanging around, perhaps from some other code you ran or maybe from before you renamed variables.

Like John said, you forgot to tell us a critical point : what the actual error was. If it says something like it doesn't know what y is (y is undefined), then you probably just forgot to pass z (instead of y) into polyfit. If you use z, it should work, like Richard said.