Plotting two variables, getting graph and x intercept

I need to plot the equation :

0 = x^3 + 6x^2 + 4(1 - y^2)

The variable y needs to take values 0, 1, 2, 3, 4. I'm wondering if there is a loop I can do for this.

I would also like to get the x-intercepts as an output.

Is there a way to plot them on single graphs and all on the same graph?

Answer 1

[Star Strider]

Try this:

xv = linspace(-6, 4, 25);
yv = [1 2 3 4];
for k = 1:numel(yv)
    ply = [1 6 0 4*(1-yv(k).^2)];
    rts(:,k) = roots(ply);
    pv(k,:) = polyval(ply, xv);
end

figure
plot(xv, pv)
grid

The x-intercepts will be the roots, returned column-wise in the ‘rts’ matrix.

[M K]

This worked beautifully! Thank you!

[Star Strider]

As always, my pleasure!

Answer 2

[Alan Stevens]

Here's an alternative

f = @(x,y) x.^3 + 6*x.^2 + 4*(1-y.^2);
coeff = @(y) [1 6 0 4*(1-y.^2)];
y = 0:4;
for i = 1:length(y)
    R(:,i) = roots(coeff(y(i)));
end
ezplot(f)

[M K]

Thank you for the alternative!