mixed partial derivatives

*To*: mathgroup at smc.vnet.net*Subject*: [mg91256] mixed partial derivatives*From*: Narasimham <mathma18 at hotmail.com>*Date*: Tue, 12 Aug 2008 04:45:30 -0400 (EDT)

When mixed derivatives are not allowed, what is the fix? TIA p=D[X[u,v],u]; q=D[X[u,v],v]; r =D[X[u,v],u,u]; s=D[X[u,v],u,v]; t=D[X[u,v],v,v]; GC[u_,v_] = (r t - s^2)/(1+p^2 + q^2)^2 NDSolve[{GC[u,v]== 1, X[u, 0] == Cosh[u], Derivative[0,1][X][u, 0] == 0, X[-3, v] == X[3, v]},X[u,v], {u,0,3},{v,0,3}] Narasimham