Plot the part of the cylinder x^2 + z^2 = 1 for y ≥ 0 , 0 ≤ z ≤ − y^2 + 1 . Can someone help me

i don't know how to do it

[Jan]

What have you tried so far?

Answer 1

[DGM]

This is a rather simple approach:

n = 200;

th = linspace(0,pi,n);
x = linspace(-1,1,n);
y = linspace(0,1,n).';

zc = repmat(sin(th),[n 1]);
xc = cos(th);
zp = repmat(-y.^2+1,[1 n]);
zc(zc>zp) = NaN;

surf(xc,y,zc); hold on

shading flat
axis equal

If you want to be assured that the trimmed face follows a parabola:

n = 200;

th = linspace(0,pi,n);
x = linspace(-1,1,n);
y = linspace(0,1,n).';

zc = repmat(sin(th),[n 1]);
xc = cos(th);

zp = repmat(-y.^2+1,[1 n]);
zc(zc>zp) = NaN;

surf(xc,y,zc); hold on
surf(x,y,zp,'facealpha',0.4);

shading flat
axis equal