RtR_prior_elem2nodes

 RtR_PRIOR_ELEM2NODES: Convert elem to nodal RtR Image Prior
 Reg= RtR_prior_elem2nodes( inv_model)
 Reg        => output regularization term
 inv_model  => inverse model struct
 Parameters:
   inv_model.RtR_prior_elem2nodes.RtR_prior= func which calcs prior
   inv_model.RtR_prior_elem2nodes.fwd_model= fwd model for elem2nodes

0001 function Reg= RtR_prior_elem2nodes( inv_model )
0002 % RtR_PRIOR_ELEM2NODES: Convert elem to nodal RtR Image Prior
0003 % Reg= RtR_prior_elem2nodes( inv_model)
0004 % Reg        => output regularization term
0005 % inv_model  => inverse model struct
0006 % Parameters:
0007 %   inv_model.RtR_prior_elem2nodes.RtR_prior= func which calcs prior
0008 %   inv_model.RtR_prior_elem2nodes.fwd_model= fwd model for elem2nodes
0009 
0010 % (C) 2008 Andy Adler. License: GPL version 2 or version 3
0011 % $Id: RtR_prior_elem2nodes.m 3040 2012-06-06 15:20:40Z aadler $
0012 
0013 NtoE = mapper_nodes_elems( inv_model.RtR_prior_elem2nodes.fwd_model );
0014 
0015 Reg_e= feval(inv_model.RtR_prior_elem2nodes.RtR_prior, inv_model);
0016 Reg= NtoE*Reg_e*NtoE';
0017 
0018 nn= size(NtoE,1);
0019 % Sometimes NtoE is singular. We use a cheap test here, because it
0020 %   is a structured matrix, and we don't want to use cond or condest
0021 % Use a NOSER type prior, because its not quite clear how to
0022 %   regularize in this case.
0023 singular = det(NtoE(:,1:nn))<1e-13;
0024 if singular
0025    hp = 1e-6;
0026    dReg= hp*spdiags(Reg,0);
0027    Reg= Reg + spdiags(dReg,0,nn,nn);
0028 end