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PONew communicator invalid MPI
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copied!<p>I want to create a new communicator that holds on to only the ranks that are used in the processing, if I have 24 processors available and I only need 10 then the group should only hold those 10, otherwise it will hold all of them. For some reason, when I attempt to create a communicator everything executes, but as soon as I try something like getting the size or rank of the new communicator MPI stops with an error.</p> <pre><code> 80 float **matrix; 81 int *ranksArr; 82 MPI_Comm default_comm; 83 MPI_Group world_grp, new_grp; 84 MPI_Comm_rank(MPI_COMM_WORLD, &proc_rank); 85 MPI_Comm_size(MPI_COMM_WORLD, &proc_avail); 86 MPI_Comm_group(MPI_COMM_WORLD, &world_grp); 91 compute_block_size(&block, proc_avail); 92 93 if(block.procsUsed == proc_avail) 94 { 95 ranksArr = alloc_ranks_arr(proc_avail); 96 } 97 else 98 { 99 ranksArr = alloc_ranks_arr(block.procsUsed); 100 proc_avail = block.procsUsed; 101 } 102 103 MPI_Group_incl(world_grp, proc_avail, ranksArr, &new_grp); 104 MPI_Comm_create(MPI_COMM_WORLD, new_grp, &default_comm); 105 //MPI_Comm_size(default_comm, &proc_avail); //ERROR, default_comm 106 107 MPI_Comm_rank(default_comm, &proc_rank); 108 111 matrix = create_matrix_sub(&block, proc_rank); 112 113 114 dealloc_matrix(matrix); 178 int* alloc_ranks_arr(int totalRanks) 179 { 180 int *ranksToGroup = malloc(totalRanks * sizeof(int)); 181 int i; 182 183 for(i = 0; i < totalRanks ; i++) 184 { 185 ranksToGroup[i] = i; 186 } 187 188 return ranksToGroup; 189 } </code></pre> <blockquote> <p>[cluster-srv2:24701] <strong>* An error occurred in MPI_Comm_rank [cluster-srv2:24701] *</strong> on communicator MPI_COMM_WORLD [cluster-srv2:24701] <strong>* MPI_ERR_COMM: invalid communicator [cluster-srv2:24701] *</strong> MPI_ERRORS_ARE_FATAL (your MPI job will now abort)</p> </blockquote> <p>It says in the docs : </p> <blockquote> <p>MPI_ERR_COMM Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).</p> </blockquote> <p>But I create the communicator right before calling Comm_rank and also the return value of MPI_Comm_create is giving me MPI_SUCCESS. So I have no idea why this is happening.</p>

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