Homework 2
In an MPI program with 8 processes, what is the smallest rank that any process will have?
0
When running an MPI program with 8 processes that call MPI_Gather using the default communicator, how many processes will receive the data?
1 Gathers data from all processes on destination process
When running an MPI program with 8 processes that call MPI_Bcast using the default communicator where the source process sends an array of 10 elements, how many elements does each destination process receive?
10
When running an MPI program with 8 processes that call MPI_Reduce using the default communicator where each source process sends an array of 10 elements, how many elements does the destination process receive?
10
When running an MPI program with 8 processes that call MPI_Scatter using the default communicator where the source process scatters an array of 16 elements, how many elements does each destination process receive?
2
In an MPI program with 8 processes, what is the largest rank that any process will have?
7
When running an MPI program with 8 processes that call MPI_Scatter using the default communicator, how many processes will receive a chunk of the data?
8 Scatter sends a chunk to each process
When running an MPI program with 8 processes that call MPI_Gather using the default communicator where each source process sends an array of 10 elements, how many elements does the destination process receive?
80
MPI programs have to be run with more than one process.
False
MPI_Allgather performs many-to-one communication.
False
MPI_Allreduce can be emulated with MPI_Reduce followed by MPI_Scatter.
False
MPI_Allreduce performs many-to-one communication.
False
MPI_Bcast performs many-to-one communication.
False
MPI_Gather performs one-to-many communication.
False
MPI_Recv may return before the message has actually been received.
False
MPI_Recv performs one-to-many communication.
False
MPI_Reduce implies a barrier.
False
MPI_Reduce performs one-to-many communication.
False
MPI_Scatter performs many-to-one communication.
False
MPI_Send performs one-to-many communication.
False
MPI_Ssend performs many-to-one communication.
False
Returning from an MPI_Gather call by any process implies that the process receiving the gathered result has already reached its MPI_Gather call.
False
The MPI_Scatter function concatenates the data from all involved processes?
False
The receive buffer size parameter in MPI_Recv calls specifies the exact length of the message to be received (in number of elements).
False # of elements in the message MPI_Recv( &buf, int buf size(#elements), datatype, source rank, message tag, comm, status)
In the call MPI_Reduce(a, z, n, MPI_DOUBLE, MPI_SUM, 8, MPI_COMM_WORLD), process 0 is the destination.
False Destination rank is 8
In the call MPI_Reduce(a, z, n, MPI_DOUBLE, MPI_SUM, 8, MPI_COMM_WORLD), each process contributes 8 elements to the reduction.
False Has n elemnts
In the call MPI_Reduce(a, z, n, MPI_DOUBLE, MPI_SUM, 8, MPI_COMM_WORLD), the result is written into the "n" array.
False Written to the "z" receive buffer(array)
A cyclic distribution of the elements in an array is useful for load balancing when the amount of work per element increases with increasing array indices.
True
A single call to MPI_Reduce by each process suffices to reduce local histograms with many buckets into a global histogram.
True
In MPI_Gather, every process has to pass a parameter for the destination buffer, even processes that will not receive the result of the gather.
True
In MPI_Gather, rank 0 always contributes the first chunk of the result.
True
MPI programs can suffer from indeterminacy.
True
MPI_Allgather implies a barrier.
True
MPI_Allgather is typically faster than calling MPI_Gather followed by MPI_Bcast.
True
MPI_Reduce has a similar communication pattern (sends and receives of messages) as MPI_Gather.
True
MPI_Reduce may be non-blocking on more than one of the involved processes.
True
MPI_Send may return before the message has actually been sent.
True
MPI_Ssend implies some synchronization.
True
Multidimensional C/C++ arrays are stored row by row in main memory.
True
Sending one long message in MPI is typically more efficient than sending multiple short messages with the same total amount of data.
True
The MPI_Barrier call requires a parameter (to be passed to the function).
True
The communication pattern (one-to-one, one-to-many, many-to-one, or many-to-many) of MPI_Gather and MPI_Reduce are identical.
True
The collatz code from the project is likely to suffer from load imbalance.
True The fractal code does as well
