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fei_LinearDecomposition.hpp
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00004 //             FEI: Finite Element Interface to Linear Solvers
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00041 */
00042 
00043 #ifndef _fei_LinearDecomposition_hpp_
00044 #define _fei_LinearDecomposition_hpp_
00045 
00046 #include <fei_macros.hpp>
00047 #include <fei_CommUtils.hpp>
00048 
00049 namespace fei {
00050 
00051 template<typename GlobalIDType>
00052 class LinearDecomposition {
00053 public:
00054   LinearDecomposition(int localProc, int numProcs,
00055                       GlobalIDType lowest_global_id,
00056                       GlobalIDType highest_global_id);
00057   ~LinearDecomposition() {}
00058 
00059   GlobalIDType first_local_id() const {return first_local;}
00060   GlobalIDType last_local_id() const {return last_local;}
00061 
00062   GlobalIDType first_global_id() const {return first_global;}
00063   GlobalIDType last_global_id() const {return last_global;}
00064 
00068   int which_proc(GlobalIDType id) const;
00069 
00070 private:
00071   GlobalIDType first_global;
00072   GlobalIDType last_global;
00073   GlobalIDType first_local;
00074   GlobalIDType last_local;
00075   std::vector<GlobalIDType> proc_offsets;
00076 };//class LinearDecomposition
00077 
00078 template<typename GlobalIDType>
00079 LinearDecomposition<GlobalIDType>::LinearDecomposition(int localProc, int numProcs,
00080                                      GlobalIDType lowest_global_id,
00081                                      GlobalIDType highest_global_id)
00082  : first_local(0),
00083    last_local(0),
00084    proc_offsets()
00085 {
00086   GlobalIDType num_global = highest_global_id - lowest_global_id + 1;
00087   GlobalIDType num_local = num_global/numProcs;
00088   GlobalIDType remainder = num_global%numProcs;
00089 
00090   //First have each entry in proc_offsets contain the number of local ids:
00091   proc_offsets.assign(numProcs, num_local);
00092   for(GlobalIDType i=0; i<remainder; ++i) {
00093     ++proc_offsets[i];
00094   }
00095 
00096   //Now convert proc_offsets so that proc_offsets[i] is the i-th proc's
00097   //offset into the global space of ids:
00098   GlobalIDType offset = 0;
00099   for(size_t i=0; i<proc_offsets.size(); ++i) {
00100     GlobalIDType tmp = proc_offsets[i];
00101     proc_offsets[i] = offset;
00102     offset += tmp;
00103   }
00104 
00105   first_global = lowest_global_id;
00106   last_global = highest_global_id;
00107   first_local = lowest_global_id  + proc_offsets[localProc];
00108   last_local  = highest_global_id + proc_offsets[localProc] + num_local - 1;
00109 }
00110 
00111 template<typename GlobalIDType>
00112 int LinearDecomposition<GlobalIDType>::which_proc(GlobalIDType id) const
00113 {
00114   if (id < first_global || id > last_global) return -1;
00115 
00116   for(size_t i=1; i<proc_offsets.size(); ++i) {
00117     if (first_global+proc_offsets[i] > id) return i-1;
00118   }
00119 
00120   int last_proc = proc_offsets.size() - 1;
00121   return last_proc;
00122 }
00123 
00124 }//namespace fei
00125 
00126 #endif
00127 
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