# psb_amx — Global maximum absolute value

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#### 7.13 psb_amx — Global maximum absolute value

call psb_amx(icontxt, dat, root)

This subroutine implements a maximum absolute value reduction operation based on the underlying communication library.

Type:
  Synchronous.
On Entry
icontxt
  the communication context identifying the virtual parallel machine.
  Scope: global.
  Type: required.
  Intent: in.
  Specified as: an integer variable.
dat
  The local contribution to the global maximum.
  Scope: local.
  Type: required.
  Intent: inout.
  Specified as: an integer, real or complex variable, which may be a scalar, or a rank 1 or 2 array. Type, kind, rank and size must agree on all processes.
root
  Process to hold the final value, or -1 to make it available on all processes.
  Scope: global.
  Type: optional.
  Intent: in.
  Specified as: an integer value -1 <= root <= np - 1, default -1.

On Return
dat
  On destination process(es), the result of the maximum operation.
  Scope: global.
  Type: required.
  Intent: inout.
  Specified as: an integer, real or complex variable, which may be a scalar, or a rank 1 or 2 array. Type, kind, rank and size must agree on all processes.

Notes

1. The dat argument is both input and output, and its value may be changed even on processes different from the final result destination.
2. The dat argument may also be a long integer scalar.

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