How do I plot a polynomial equation and set of x-y coordinates on the same graph?
9 views (last 30 days)
Show older comments
I am trying to plot a polynmial and some x-y coordinates on the same graph. I need the coordinates to be visible and the lines to be distingushable from one another (eg. different colors).
Here is the measured data.
coefficients = [0.6252 -0.4165 0.1311 -0.0163 0.0009,-0.0000]
x = [2 5 8 11 14 20];
y = [0.20 0.29 0.44 0.50 0.66 0.56];
0 Comments
Accepted Answer
Sam Chak
on 10 May 2024
Edited: Sam Chak
on 10 May 2024
Edit: Your original polynomial coefficients are truncated. So, the polynomial cannot produce an accurate result.
%% data
x = [2 5 8 11 14 20];
y = [0.20 0.29 0.44 0.50 0.66 0.56];
%% polynomial coefficients
coefficients = [0.6252 -0.4165 0.1311 -0.0163 0.0009 -0.0000];
p = fliplr(coefficients)
format long
p = polyfit(x, y, numel(x)-1)
%% points generated by polynomial
xx = linspace(x(1), x(end), 181);
yy = polyval(p, xx);
%% plot results
plot(x, y, 'o', 'markersize', 10), hold on
plot(xx, yy), grid on, xlabel('x'), xlabel('y')
legend('data', 'polynomial', 'location', 'northwest')
9 Comments
Sam Chak
on 11 May 2024
Edited: John Kelly
on 20 May 2024
Hi
You can use the polyval() command in this case.
%% data
x = [2 5 8 11 14 20];
y = [0.20 0.29 0.44 0.50 0.66 0.56];
%% polynomial coefficients
p = polyfit(x, y, numel(x)-1)
%% points generated by polynomial
xx = linspace(x(1), x(end), 181);
yy = polyval(p, xx);
%% find y coordinate with given x coordinate
xpt = 17.5;
ypt = polyval(p, xpt)
%% plot results
plot(x, y, 'o', 'markersize', 10), hold on
plot(xx, yy), grid on, xlabel('x'), ylabel('y')
plot(xpt, ypt, 'p', 'markersize', 10, 'color', "#7E2F8E"), hold off
legend('data', 'polynomial', 'point', 'location', 'northwest')
More Answers (1)
KSSV
on 10 May 2024
x = [2 5 8 11 14 20];
y = [0.20 0.29 0.44 0.50 0.66 0.56];
p = polyfit(x,y,3) ;
yi = polyval(p,x) ;
figure
hold on
plot(x,y,'r')
plot(x,yi,'b')
legend('data points','polynomial fit')
0 Comments
See Also
Categories
Find more on Interpolation in Help Center and File Exchange
Products
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!