Question: Get derivative

Help me please, How to get a spatial derivative?After solving a system of differential equations numerically, I got module.Help please, How can I find a  value of the first derivative
For example , after solving the PDE system, module() export plot,plot3d,animate,value,settings; ... end module
So, I need to find diff(U(x,t),x) (for example x=0 and t=0) 

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