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diis.h

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+//DIIS convergence acceleration
+#ifndef _DIIS_H_
+#define _DIIS_H_
+#include "vec.h"
+#include "smat.h"
+#include "mat.h"
+#include "sparsemat.h"
+#include "nonclass.h"
+#include "la_traits.h"
+#include "auxstorage.h"
+
+// T is some solution vector in form of NRVec, NRMat, or NRSMat over double or complex<double> fields
+
+template<typename T>
+class DIIS
+	{
+	int dim;
+	int aktdim;
+	bool incore;
+	int cyclicshift; //circular buffer of last dim vectors
+	typedef typename LA_traits<T>::elementtype Te;
+	NRSMat<Te> bmat;
+	AuxStorage<Te> *st;
+	T *stor;
+public:
+	DIIS(const int n, const bool core=1);
+	~DIIS();
+	Te extrapolate(T &vec); //vec is input/output; returns square residual norm
+	};
+
+template<typename T>
+DIIS<T>::DIIS(const int n, const bool core) : dim(n), incore(core), bmat(n+1,n+1)
+{
+st=incore?NULL: new AuxStorage<Te>;
+stor= incore? new T[dim] : NULL;
+bmat= (Te)0; for(int i=1; i<=n; ++i) bmat(0,i) = (Te)-1; 
+aktdim=cyclicshift=0;
+
+}
+
+template<typename T>
+DIIS<T>::~DIIS()
+{
+if(st) delete st;
+if(stor) delete[] stor;
+}
+
+
+template<typename T>
+typename DIIS<T>::Te DIIS<T>::extrapolate(T &vec)
+{
+//if dim exceeded, shift 
+if(aktdim==dim)
+	{
+	cyclicshift=(cyclicshift+1)%dim;
+	for(int i=1; i<dim; ++i)
+		for(int j=1; j<=i; ++j)
+			bmat(i,j)=bmat(i+1,j+1);
+	}
+else
+	++aktdim;
+
+//store vector
+if(incore) stor[(aktdim-1+cyclicshift)%dim]=vec;
+else st.put(vec,(aktdim-1+cyclicshift)%dim);
+
+//calculate overlaps
+bmat(aktdim,aktdim)= vec.dot(vec);
+if(incore)
+	for(int i=1; i<aktdim; ++i) bmat(i,aktdim)=vec.dot(stor[(i-1+cyclicshift)%dim]);
+else
+	{
+	T tmp=vec; //copy dimensions
+	for(int i=1; i<aktdim; ++i) 
+		{
+		st.get(tmp,(i-1+cyclicshift)%dim);
+		bmat(i,aktdim)=vec.dot(tmp);
+		}
+	}
+
+//prepare rhs-solution vector
+NRVec<Te> rhs(dim+1);
+rhs= (Te)0; rhs[0]= (Te)-1;
+
+//solve for coefficients
+{
+NRSMat<Te> amat=bmat;
+linear_solve(amat,rhs,NULL,aktdim+1);
+}
+
+//build the new linear combination
+vec.copyonwrite();
+vec *= rhs[aktdim];
+if(incore)
+	for(int i=1; i<aktdim; ++i) vec.axpy(rhs[i],stor[(i-1+cyclicshift)%dim]);
+else
+        {
+	T tmp=vec; //copy dimensions
+	for(int i=1; i<aktdim; ++i)
+                {
+                st.get(tmp,(i-1+cyclicshift)%dim);
+		vec.axpy(rhs[i],tmp);
+                }
+        }
+
+return rhs[0];
+}
+
+
+#endif