Hi, So in 3d if U, V, W being the displacements in X, Y and Z directions and if I want to use fe_values.shape_grad(i,q) to write Ux + Uy - Wz, how do I differentiate between (U,V,W) and (X,Y,Z). I would like to clarify my confusion here because I am trying to solve an equation which has 4 individual components (say U, V, W, H) with spatial derivatives in (X, Y, Z) mixed up just like Ux + Uy - Wz.
Thanks ! Arun. On Sun, May 9, 2010 at 5:26 PM, arun jaganathan <[email protected]> wrote: > Thanks Wolfgang. > > Arun. > > > On Sun, May 9, 2010 at 2:07 PM, Wolfgang Bangerth > <[email protected]>wrote: > >> >> Arun, >> >> > Can someone tell me how to use shape_grad() to the get the gradient in >> > only a particular direction ? Using tutorial programs I figured out how >> > to get the derivative of the shape function for individual components >> > but unsure how to use shape_grad() to get the derivative in a particular >> > direction (say Ux + Uy - Vz with U and V being the two components). >> >> fe_values.shape_grad (i,q) returns the gradient of shape function i and >> quadrature point q, i.e. all components of the vector. If you are in 3d, >> then >> fe_values.shape_grad(i,q)[0] >> is the X-derivative (in real coordinates, not the reference coordinates of >> the cell) and >> fe_values.shape_grad(i,q)[1] >> fe_values.shape_grad(i,q)[2] >> similarly for the y and z derivatives. >> >> Best >> W. >> >> ------------------------------------------------------------------------- >> Wolfgang Bangerth email: [email protected] >> www: http://www.math.tamu.edu/~bangerth/ >> >> >
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