fn_find_interval.hpp

Go to the documentation of this file.

/*
 * BELFEM -- The Berkeley Lab Finite Element Framework
 * Copyright (c) 2026, The Regents of the University of California,
 * through Lawrence Berkeley National Laboratory (subject to receipt of any required
 * approvals from the U.S. Dept. of Energy).  All rights reserved.
 *
 * Developers: Christian Messe, Gregory Giard
 *
 * See the top-level LICENSE file for the complete license and disclaimer.
 */
 
#ifndef BELFEM_FN_FIND_INTERVAL_HPP
#define BELFEM_FN_FIND_INTERVAL_HPP
 
#include "typedefs.hpp"
#include "cl_Vector.hpp"
 
namespace belfem
{
//------------------------------------------------------------------------------
 
    inline void
    find_interval( const Vector< real > & aData, const real aValue, index_t & aIndex, real & aXi )
    {
        index_t i = 0;
        index_t k = aData.length() - 1;
        index_t j = ( i + k ) / 2 ;
 
        if( aValue <= aData( 1 ) )
        {
            aIndex = 0;
 
            aXi = ( aValue - aData( 0 ) ) / ( aData( 1 ) - aData( 0 ) );
        }
        else if ( aValue >= aData( k - 1 ) )
        {
            aIndex = k - 1;
            aXi = ( aValue - aData( k-1 ) ) / ( aData( k ) - aData( k - 1 ) ) ;
        }
        else
        {
            while ( true )
            {
                if (( aData( i ) <= aValue ) && ( aData( j ) >= aValue ))
                {
                    // this is the correct interval
                    k = j;
                }
                else
                {
                    // the other one is the correct interval
                    i = j;
                }
                if (( k - i ) == 1 )
                {
                    aIndex = i;
                    aXi = ( aValue - aData( i ) ) / ( aData( k ) - aData( i ) );
                    break;
                }
                else
                {
                    j = ( i + k ) / 2 + ( i + k ) % 2;
                }
 
            }
        }
    }
 
//------------------------------------------------------------------------------
}
 
#endif //BELFEM_FN_FIND_INTERVAL_HPP