Genetic algorithm pressurized cylindrical tube

I need to make a 60x6 matrix with these variables, Force, Torque, radius, thickness, Pressure and my cost function. I can't get my cost function to work. ? = (?−2??^2)/(2??^2 )^2. The variables are as follows

?=[(?? − ??)^2+ (?? − ??)^2+ (?? − ??)^2 + 6(???^2 + ???^2 + ???^2)]

??=[((?? − ??)^2+ (?? − ??)^2+ (?? − ??)^2 + 6(???^2 + ???^2 + ???^2))/2]^.5

??=F/A

??=(P*r)/t

???=(T*r)/J

J=(pi*t*r^3)/2

A=2*pi*r*t

So far I redefined it into variables I can use and now have this,

J=(pi*t*r^3)/t;

A=pi*2*r*t;

a=((b-c)^2 +(c-d)^2+6(e^2 +f^2 +g^2))/2)^.5

b=F/A;

c=(P*r)/t;

d=(p*r)/J;

e=(t*r)/J;

f=(t*r)/J;

g=(t*r)/J;

y=((b-c)^2 +(c-d)^2+6(e^2 +f^2 +g^2));

z=((y-2a^2)/(2a^2))^2;

I get an error with this.