plot 3d curve with conditions

Hi everyone,

I would like to plot a 3D curve in the form of y=f(x,y) with two conditions on x and y ( x>2*y and y<100-x/2)

Can someone help me to code it?

Thank you

Answer 1

[Star Strider]

Not certain what you want, but this seems to work:

x = linspace(-9, 9);
y = linspace(-9, 9);

f = @(x,y) x.^2 .* cos(2*pi*y);

[X1,Y1] = meshgrid(x(x<2*y), y);

[X2, Y2] = meshgrid(x, y);

F1 = f(X1, Y1);
F2 = f(X2,Y2);

figure(1)
mesh(X1, Y1, F1)
grid on
xlabel('x')
ylabel('y')
title('f(x>2\cdoty,y)')

figure(2)
mesh(X2, Y2, F2)
grid on
xlabel('x')
ylabel('y')
title('f(x,y)')

Adding the second constraint:

y = linspace(-9, 9);

f = @(x,y) x.^2 .* cos(2*pi*y);

[X1,Y1] = meshgrid(x(x<2*y), y(y<100-x/2));

[X2, Y2] = meshgrid(x, y);

F1 = f(X1, Y1);
F2 = f(X2,Y2);

figure(1)
mesh(X1, Y1, F1)
grid on
xlabel('x')
ylabel('y')
title('f(x>2\cdoty, y<100\cdotx/2)')

figure(2)
mesh(X2, Y2, F2)
grid on
xlabel('x')
ylabel('y')
title('f(x,y)')

Answer 2

[John D'Errico]

I would triangulate the domain of interest. Then I would use one of the tools that can build a contour plot from that triangulated domain, where the only contour is at zero, thus

y - f(x,y) == 0

There are several tricontour tools on the file exchange.

The fact is though, this is not a 3-d curve,and your question explicitly states that as a goal. So I'm not sure what your goal really is.