## 5.3.4. Reserved Keys

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The following keys are reserved. An implementation is not required to interpret these keys, but if it does interpret the key, it must provide the functionality described.

{ host}
  Value is a hostname. The format of the hostname is determined by the implementation.

{ arch}
  Value is an architecture name. Valid architecture names and what they mean are determined by the implementation.

{ wdir}
  Value is the name of a directory on a machine on which the spawned process(es) execute(s). This directory is made the working directory of the executing process(es). The format of the directory name is determined by the implementation.

{ path}
  Value is a directory or set of directories where the implementation should look for the executable. The format of path is determined by the implementation.

{ file}
  Value is the name of a file in which additional information is specified. The format of the filename and internal format of the file are determined by the implementation.

{ soft}
  Value specifies a set of numbers which are allowed values for the number of processes that MPI_COMM_SPAWN (et al.) may create. The format of the value is a comma-separated list of Fortran-90 triplets each of which specifies a set of integers and which together specify the set formed by the union of these sets. Negative values in this set and values greater than maxprocs are ignored. MPI will spawn the largest number of processes it can, consistent with some number in the set. The order in which triplets are given is not significant.

  By Fortran-90 triplets, we mean:

  1. `a` means a
  2. `a:b` means a, a+1, a+2, ..., b
  3. `a:b:c` means a, a+c, a+2c, ..., a+ck, where for c > 0, k is the largest integer for which and for c < 0, k is the largest integer for which . If b > a then c must be positive. If b < a then c must be negative.
  Examples:
  1. `a:b` gives a range between a and b
  2. `0:N` gives full ``soft'' functionality
  3. `1,2,4,8,16,32,64,128,256,512,1024,2048,4096` allows power-of-two number of processes.
  4. `2:10000:2` allows even number of processes.
  5. `2:10:2,7` allows 2, 4, 6, 7, 8, or 10 processes.

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