> A:=matrix(2,2):

> A[1,1]:=1+exp(2*kappa1*x+2*kappa1^3*t+2*theta1)/(2*kappa1):

> A[2,2]:=1+exp(2*kappa2*x+2*kappa2^3*t+2*theta2)/(2*kappa2):

> A[1,2]:=exp((kappa1+kappa2)*x+(kappa1^3+kappa2^3)*t+theta1+theta2)/(kappa1+kappa2):

> A[2,1]:=A[1,2]:

> print(A);

> u:=simplify(-2*diff(log(det(A)),x,x));

> simplify(diff(u,t)-1/4*diff(u,x,x,x)+3/2*diff(u,x)*u);

0