### psb_cd_set_large_threshold -- Set threshold for index mapping switch

    call psb_cd_set_large_threshold(ith)

Type:
  Synchronous.
On Entry
ith
  the new threshold for communication descriptors.
  Scope: global.
  Type: required.
  Intent: in.
  Specified as: an integer value greater than zero.

Note: the threshold value is only queried by the library at the time a call to `psb_cdall` is executed, therefore changing the threshold has no effect on communication descriptors that have already been initialized. Moreover the threshold must have the same value on all processes.