inertia_tensor=inertia(a_matrix)

function inertia_tensor=inertia(a_matrix)

inertia_tensor(1,2)=-sum(a_matrix(:,1).*a_matrix(:,2));
inertia_tensor(2,1)=inertia_tensor(1,2);
inertia_tensor(1,3)=-sum(a_matrix(:,1).*a_matrix(:,3));
inertia_tensor(3,1)=inertia_tensor(1,3);
inertia_tensor(2,3)=-sum(a_matrix(:,2).*a_matrix(:,3));
inertia_tensor(3,2)=inertia_tensor(2,3);
inertia_tensor(1,1)=sum((a_matrix(:,2)).^2+(a_matrix(:,3)).^2);
inertia_tensor(2,2)=sum((a_matrix(:,1)).^2+(a_matrix(:,3)).^2);
inertia_tensor(3,3)=sum((a_matrix(:,1)).^2+(a_matrix(:,2)).^2);