#ifndef HAMILTON_INCLUDED
#define HAMILTON_INCLUDED

#include "basis.h"

/*
   Structure to hold matrix elements of a sparse Hamiltonian.
   Here, we use "symmetric column pointer format" as suggested
   in the Cray "man intro_sparse" pages.
   Proper initialization is {NULL,NULL,NULL,NULL,0,0,0,0,0}
   Here we include only one triangle of the matrix, assuming symmetry.
   The array j is length n+1 and
   els.j[els.n] contains the length of els.e and els.i.  

   The structure can also hold a complex matrix.  The pointer
   for the complex matrix points to the same memory.  The pointer
   not being used is set to null.

   The pointers could be "size_mem" but they are never passed
   over mpi.  If size_mem is larger than size_t then memory is wasted.
*/


typedef struct { 
  element *r;         /* The elements of the matrix */
  complex_element *c; /* The elements of the matrix in the case of a
                          complex matrix */
  size_t *i;   /* The corresponding column of that element */
  size_t *j;   /* The position in the above list of each row of the matrix */
  size_t rc_length; /* bytes of memory allocated for els.r or els.c */ 
  size_t i_length;  /* bytes of memory allocated for els.i */ 
  size_t j_length;  /* bytes of memory allocated for els.j */
  size_t n;         /* Size of the matrix */
} elslist;


/************* Prototypes for functions in hamilton.c ***************/

void hamels(elslist *els, full_basis *,element *couplings);
void hamelsc(elslist *els, full_basis *x, element *couplings);
                  /* make a list of nonzero matrix elements for nonzero 
		     transverse momentum.  */
void print_els(elslist *els, int);  /* print some nonzero matrix elements */
void free_els(elslist *els);  /* free memory used by els */

#endif