Secure, that best guess for max_blocks is always >= 1

[mhrib]

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Pull request version of issue #426

PR checklist

• [x ] Short (1 sentence) summary of your PR:
  Secure, that best guess for max_blocks is always >= 1. Replace issue ice_domain.f90: Secure max_blocks >= 1 for "best max_block estimate" #426
• [x ] Developer(s):
  Mads Hvid Ribergaard @mhrib
• [ x] Suggest PR reviewers from list in the column to the right.
  @apcraig
• Please copy the PR test results link or provide a summary of testing completed below.
  ENTER INFORMATION HERE
• How much do the PR code changes differ from the unmodified code?
  • [x ] bit for bit
  • different at roundoff level
  • more substantial
• Does this PR create or have dependencies on Icepack or any other models?
  • Yes
  • [x ] No
• Does this PR add any new test cases?
  • Yes
  • [ x] No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/. A test build of the technical docs will be performed as part of the PR testing.)
  • Yes
  • [x ] No, does the documentation need to be updated at a later time?
    • Yes
    • [x ] No
• [ x] Please provide any additional information or relevant details below:
  Replace issue ice_domain.f90: Secure max_blocks >= 1 for "best max_block estimate" #426

[eclare108213]

Looks okay to me. What is the case that fails without this line?

[mhrib]

Eg. one single block:
block_size_x=nx_global
block_size_y=ny_global

I do not recall why -/+1 arrise in the following line just prioir to the suggested added line. Maybe something with halos...:
max_blocks=int( &
( (dble(nx_global-1)/dble(block_size_x + 1)) * &
(dble(ny_global-1)/dble(block_size_y + 1)) ) &
/ dble(nprocs))

Could also change this line and exclude the 4 times +/-1 's.

[apcraig]

I ran a full test suite on conrad, 4 compilers, with no problems (as expected).