{convex}*{real affine}

 cvx_begin 
 variable Q(N,3) 
for n=1:1:N-1  
eta(n,:)=1+(((1/2)*(norm(Q(n+1,:)-Q(n,:))*(Q(n+1,3)-Q(n,3)))*d0*rho*S*chi)/(delta_t^2*W));
end

Disciplined convex programming error:
Cannot perform the operation: {convex} .* {real affine}

I will presume this is non-convex unless ypu prove otherwise.