I don't know where my code is wrong

This is a code that I wrote. I'm new with matlab so I'm not used to all the grammers and stuffs.

It keeps says 'Invalid expression. When calling a function or i....etc' when I try to run the code. I don't really know how to fix it.

theta=linspace(0,pi/2,256);
k=linspace(-10,10,256);
for i=1:256;
    for j=1:256;
        syms f(x,y)
        f(x,y) = piecewise( (x^2+y^2<=1 & y*tan(theta(i))+k(j)>0),y*tan(theta(i))+k(j),0)
        g(x,y)=y*f(x,y);
        volume=integral2(f,-1,1,-1,1);
        xcm=0;
        ycm=integral2(g,-1,1,-1,1);
        zxm=volume/pi;
        height=2*(ycm+zcm*tan(theta(i));

Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

        epsilon(length(epsilon)+1)=volume/(pi*height);
        distance(length(distance)+1)=(ycm^2+(0.5*height-zcm)^2)^0.5
    end
end
plot(epsilon, distance);

[Jan]

Whenever you mention an error in the corum, post a copy of the complete message.

I've edited your code and ran it to show, where the message occurs.

Answer 1

[Voss]

This line:

height=2*(ycm+zcm*tan(theta(i));
%        1           2     3 21

is missing a close parenthesis ) somewhere.

Answer 2

[Torsten]

If

 x = r, y = theta and z = z,

the volume of the cylinder below the plane

2x - y + 2z = 2

down to zmin can be calculated as

fun = @(x,y,z) x;
xmin = 0.0;
xmax = 1.0;
ymin = 0.0;
ymax = 2*pi;
zmin = -0.5;  % e.g.
zmax = @(x,y) 1 + 0.5*x.*sin(y) - x.*cos(y);
Volume = integral3(fun,xmin,xmax,ymin,ymax,zmin,zmax)

[서준 장]

Thank you so much for your help, It helped a lot.

I wanted to change your code a little bit since I wanted to focus on the area which z>0.

fun = @(x,y,z) x;

xmin = 0.0;

xmax = 1.0;

ymin = 0.0;

ymax = 2*pi;

zmin = -0.5; % e.g.

zmax = @(x,y) piecewise( (1 + 0.5*x.*sin(y) - x.*cos(y))>0, 1 + 0.5*x.*sin(y) - x.*cos(y),0);

Volume = integral3(fun,xmin,xmax,ymin,ymax,zmin,zmax)

Volume =

A lot of errors when I ran this code. Is there an error in 'zmax=@(x,y) pi......' ??

Thank you

[Torsten]

And just changing

zmin = -0.5

to

zmin = 0.0

and

zmax = @(x,y) 1 + 0.5*x.*sin(y) - x.*cos(y);

to

zmax = @(x,y) max(0, 1 + 0.5*x.*sin(y) - x.*cos(y));

is not what you want ?

[서준 장]

yes yes this is excacly what I was looking for.

I was kind of confused.

I don't know how to thank you..

Thank you sooo much.. have a nice day, from a student from south korea

[Torsten]

Greetings back from Germany.