Finite difference (cont'd)

• Where are the data? (cont'd)
  • Message passing with domain decomposition
    
    
    • , may be on different PE(s) than

    • Need for neighbor PE's outer data leads to guard points
      
      

    • Communicate all guard layers in one message, then use local values for all F.D. calculations.

                parameter (nx=20,p=4,ng=2)
                real f(1:nx/p+2*ng)
                real fdprime(1:nx/p+2*ng)
                do i=(ng+1),(nx/p+2*ng),1
                 fdprime(i)= c0*(-f(i+2)+ 16*f(i+1)
                               30*f(i)  + 16*f(i-1) -
                                  f(i-2))
                enddo
      

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