MATLAB: Linear fit of the points

curve fittinglinear fit

Hello, I got a plot (attached). Suppose the plot is simply from:

plot (x,y);

How can I get a linear least squares fit for these three points (they are actually not on one line) and then get the specific x values on the fit when I give certain y values, for example:

2.5:0.025:2.55

Thank you very much!

Best Answer

Probably the easiest way is to use polyfit and polyval. Use an order 1 polynomial to get a straight-line fit.

EDIT— To get the x-values for y-values using polyfit for a straight-line fit, this will work:

b = polyfit(x, y, 1);
x = (y-b(2))/b(1);

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MATLAB: Intersection of line and curve from thier points

Try this:

x_line = [7020 0];
y_line = [0 250000];
x_curve = [5620 4850 4290 3600];
y_curve = [0 100000 200000 300000];
b_line = polyfit(x_line, y_line,1);                     % Fit ‘line’
y_line2 = polyval(b_line, x_curve);                     % Evaluate ‘line’ At ‘x_curve’
x_int = interp1((y_line2-y_curve), x_curve, 0);         % X-Value At Intercept
y_int = polyval(b_line,x_int);                          % Y-Value At Intercept
figure(1)
plot(x_line, y_line)
hold on
plot(x_curve, y_curve)
plot(x_int, y_int, '+r')                                % Plot Intercept Point
hold off

MATLAB: Extrapolate best-fit line

If you have the coefficients c(1) and c(2) of the fit line l(x)=c(1)+c(2)*x, just evaluate the equation at the x-coordinate of the star point and compare with the y-coordinate of the star point.

Best Answer

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MATLAB: Intersection of line and curve from thier points

MATLAB: Extrapolate best-fit line

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