1. A computer-implemented method for performing a vector collective operation on a parallel computer comprising a plurality of compute nodes, each compute node having at least a processor and a memory, the method comprising: performing a collective operation by the plurality of compute nodes to determine a plurality of displacements for the vector collective operation; generating descriptors for the vector collective operation, based on the plurality of displacements; and performing the vector collective operation by the plurality of compute nodes, using the generated descriptors.