Ellipsoid is showing as a sphere

Hello all,

I have spent the last couple hours trying to figure out why my code only shows my figure as a sphere when it is supposed to be elliptical. I've attached my code and a picture from anouther 3d website to hopefully help figure out where im messing up. Could it be the isosurface twisting my data? Thank you all who spend there time looking at ths!

clc; clear;
sig1c = -15; %always set compression as negative
sig1t = 1; %always set tension as positve
sig2c = -6;
sig2t = 1;
sig3c = -2;
sig3t = 5;

F1 = ((1/sig1t)-(1/sig1c));
F2 = ((1/sig2t)-(1/sig2c));
F3 = ((1/sig3t)-(1/sig3c));
F11 = (1/(sig1c*sig1t));
F22 = (1/(sig2c*sig2t));
F33 = (1/(sig3c*sig3t));

syms sig1 sig2 sig3 G

    [sig1,sig2,sig3] = meshgrid(linspace(-30,30,100));

    sig1b = 0;
    sig2b = 0;
    sig3b = 0;
   
     
    G = F1.*sig1 + F11.*sig1.^2 + F2.*sig2 + F22.*sig2.^2 + F3.*sig3 + F33.*sig3.^2 - 1;
    G(G>1) = 1;
    
    Stich = patch(isosurface(sig1,sig2,sig3,G,0),'Facecolor', 'none', 'Edgecolor', 'blue');
    isonormals(sig1,sig2,sig3,G,Stich)
    
    xlabel("\sigma_1");
    ylabel("\sigma_2");
    zlabel("\sigma_3");
    title('Tsai-Wu Yield Surface');
    view(3);
   
    

[DGM]

Looks ellipsoidal to me

Just set

axis equal

[Kevin Hanekom]

Turns out something simple is always better lol, thank you!

Answer 1

[Image Analyst]

Try

axis equal

or

axis square

[Kevin Hanekom]

You are amazing!! Thank you!