PDE Interface Variables

The following list shows symbolic expressions for quantities appearing in the definition of PDEs and the corresponding variable names, which can be used in PDE coefficients and are available for results evaluation and visualization

Expression	Name	Description
ui	ui	The solution variable (dependent variable)
	uixj	The derivative of the solution variable ui with respect to the spatial coordinate xj, for example, uy
	uiTxj	The xj component of the gradient of ui projected onto a boundary or edge, for example, uTy
	uixjxk	The second derivative of the solution variable ui with respect to the spatial coordinates xj and xk, for example, uxx, uxy
	uit	The derivative of the solution variable ui with respect to time
	uitt	The second derivative of the solution variable ui with respect to time
	uixjt	The mixed derivative of the solution variable ui with respect to time and the spatial coordinate xj