plot a surface for g-f=0

Hi, would you mind telling me how can I plot g-f=0 as a surface.

f=0.07.*z.^2./(0.09+z.^2) and g=0.003+0.01.*(42./(42+(y-z).^4))

Thanks in advance for any help.

Answer 1

[Star Strider]

That is challenging, however it will work with certain restrictions on the matrix dimensions (i.e. they must both be the same sizes) —

f = @(z) 0.07.*z.^2./(0.09+z.^2);
g = @(y,z) 0.003+0.01.*(42./(42+(y-z).^4)); 
N = 25;
y = linspace(-10, 10, N);
z = linspace(-10, 10, N);
[Y,Z] = ndgrid(y,z);

figure
surf(Y,Z,f(Z))
colormap(turbo)

figure
surf(Y,Z,g(Y,Z))
colormap(turbo)

figure
surf(Y,Z,g(Y,Z)-f(Z))
hold on
contour3(Y,Z,g(Y,Z)-f(Z), [0 0], '-r', 'LineWidth',2)                       % Plot Contour At 0
hold off
colormap(turbo)

.

[M]

Great, Thank you so much,

[Star Strider]

As always, my pleasure!

[Paul]

Why use ndgrid() here and not meshgrid()? Doesn't surf expect the first two arguments to be in meshgrid() format?

[Star Strider]

Either work, although the outputs are different. Some functions require meshgrid and others require ndgrid.

Answer 2

[Torsten]

The "surface" f-g = 0 is a one-dimensional manifold in the y/z - plane and you get the corresponding curves using the "fimplicit" command:

fimplicit(@(y,z)0.07.*z.^2./(0.09+z.^2)-(0.003+0.01.*(42./(42+(y-z).^4))))