MATLAB: Plot parabola with start, end and vertex points

parabolaplot parabolaplot three points

Hi,

So I have three points and I would like matlab to plot them as a parabola. The points represent the path of a balls projectile motion and I know the start (0,0), end (2.062, 0) and high point (1.031, 0,73) of the parabola.

What I would like most would be to plot these points as a parabola and also calculate the equation for the parabola.

Thanks in advance 🙂

Freyja

Best Answer

Another way to get the parabola is to write:

 y = 0.73-a*(x-1.031)^2

which is the form it must have to peak at (1.031,0,73) and then set x and y to zero to force the parabola to contain (0,0) and solve for a. The solution is obvious. Then do a plot.

Related Solutions

MATLAB: Polyfit, polyval and plot

Because the syntax should be

polyfit(x,y,N)

and not

polyfit(y,x,N)

Here is some code that illustrates the fix:

x = 1:503;

y = 250 + 0.02*x + 0.005*x.^2 + 0.2*rand(1,503).*x;

figure
polyfit(y,x,0);
coef1 = polyfit(x,y,0);
y1 = polyval(coef1,x);
hold on
plot(x,y,'.');
plot(x,y1);  
polyfit(x,y,1);
coef2 = polyfit(x,y,1);
y2 = polyval(coef2,x);
plot(x,y2);
polyfit(y,x,2);
coef3 = polyfit(x,y,2);
y3 = polyval(coef3,x);
plot(x,y3);

MATLAB: Finding values from Cubicinterp fit

Use fzero to solve f(x) = 0.5. Keep in mind you can evaluate the fit by passing it a value.

load census
populationFit = fit(cdate, pop, 'poly2');
populationIn1925 = populationFit(1925)

You can check that it evaluated the fit correctly.

plot(cdate, pop)
hold on
plot(populationFit)
plot(repmat(1925, 1, 2), ylim)
plot(xlim, repmat(populationIn1925, 1, 2))
plot(1925, populationIn1925, 'o')

Best Answer

Related Solutions

MATLAB: Polyfit, polyval and plot

MATLAB: Finding values from Cubicinterp fit

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