Error Messages, dimension and plot2cart (Matlab)

Hi the following script gives back the errors.But im not sure why

"Error using .* Matrix dimensions must agree.

Error in pol2cart (line 22) x = r.*cos(th);

Error in SurfPlotQ1 (line 18) [x,y]= pol2cart(th,r);"

 function graph=plot(c,P,rd,E,t,nu,K,w,y,r,th) ;

 c=15;
 P=15;
 rd=15;
 E=18*10^6;
 t=0.08;
 nu=0.3;

 th=meshgrid(0:0.1:2.*pi);

 w=meshgrid(0:0.1:rd);

 r=meshgrid(0:0.1:rd);

[x,y]= pol2cart(th,r);

K= (E*t^3)/(12*(1-nu^2));

 w=((P.*rd.^4)./(64.*K)).*(1-(r./rd).^2).^2+c;

mesh(x,y,w);

colorbar

end

Answer 1

[Star Strider]

Use the linspace function to generate the arguments to meshgrid to calculate ‘th’, ‘w’, and ‘r’. That way you can specify all of them to have the same lengths. That will avoid the error you’re getting.

[John Smith]

Thanks for the reply! but would i have to replace meshgrid with linspace, or just do it after meshgrid?

[Star Strider]

My pleasure!

You can do linspace outside meshgrid or inside it. It’s all the same to the computer — neither is more efficient. This should work:

th=meshgrid(linspace(0,2*pi,250));

The choice of 250 is arbitrary. Just be sure it’s the same value for all three variables and you won’t get the ‘matrix dimensions must agree’ error. (You don’t want them arguing in any event!)

[John Smith]

Now the errors are - "Error using mesh (line 76) Z must be a matrix, not a scalar or vector

Error in SurfPlotQ1 (line 29) mesh(x,y,w);" and i know its meant to look like this http://i.imgur.com/iz74iV8.jpg?1

function graph=plot(c,P,rd,E,t,nu,K,w,y,r,th) ;

 c=15;
 P=15;
 rd=15;
 E=18*10^6;
 t=0.08;
 nu=0.3;

th=meshgrid(linspace(0,2*pi,1));

 w=meshgrid(linspace(0,rd,1));

 r=meshgrid(linspace(0,rd,1));

[x,y]= pol2cart(th,r);

K= (E*t^3)/(12*(1-nu^2));

 w=((P.*rd.^4)./(64.*K)).*(1-(r./rd).^2).^2+c;

surf(x,y,w);

colorbar

end

[Star Strider]

The third argument to linspace is the length of the vector you want it to create. You’ve asked it to create a scalar with a lenght of 1, and it did!

Change the linspace calls to:

th=meshgrid(linspace(0,2*pi,100));
w=meshgrid(linspace(0,rd,100));
r=meshgrid(linspace(0,rd,100));

and it works.