how to do a line progression of line trend.

So i have a line plot from an two arrays X = [52.5, 81.25, 86.25, 106.5]; and Y= [787.5, 1228.13, 1361.25, 1796.26, 1233.75];. How am I able to map their progression if the trend where to keep on going.

Answer 1

[Star Strider]

First, you cannot, because your ‘X’ vector is (1x4) and your ‘Y’ vector is (1x5). Deleting the last element of ‘Y’, fitting a linear model, and extrapolating, try this:

X = [52.5, 81.25, 86.25, 106.5];
Y= [787.5, 1228.13, 1361.25, 1796.26];

B = [X(:) ones(size(X(:)))]\Y(:);

Xv = linspace(-100, 250);
Yv = [Xv(:), ones(size(Xv(:)))] * B;

figure(1)
plot(X, Y, 'pg')
hold on
plot(Xv, Yv, '-r')
hold off
grid

[jesus escareno]

Yes sorry about that I was missing a data point. Can you just explain what B is equal too. Thanks in advance

[Star Strider]

As always, my pleasure.

No worries!

In my code, ‘B’ are the regression coefficients. As I coded it, ‘B(1)’ is the slope, and ‘B(2)’ is the intercept of a linear regression fit to your data. It is a column vector, so multiplying it by the original design matrix (here [X(:) ones(size(X(:)))]) will produce a linear fit to your data.

I could have instead used:

B = polyfit(X, Y, 1);

and:

Yv = polyval(B, Xv);

however chose not to in order to explore a different (and for this problem, more efficient) option.

[jesus escareno]

Okay I got it. Does clarify how the whole code works.

Thanks.

[Star Strider]

As always, my pleasure.