J3/07-123 Date: 24 January 2007 To: J3 From: John Reid and Bill Long Subject: Note on shared-memory implementation Reference: J3/07-007 Discussion The second sentence of NOTE 2.9: "On a shared-memory machine, a co-array could be implemented as a section of an array of higher rank." is not correct. For a simple example, suppose there are 2 images, an actual argument is a co-array declared with dimension (3) and the corresponding dummy argument is a co-array declared with dimension (2,*). In array element order, the entries of the dummy co-array on the two images are a(1,1)[1] a(2,1)[1] a(1,2)[1] a(1,1)[2] a(2,1)[2] a(1,2)[2] No array of rank 3 has elements missing like this. For another example, suppose the actual argument is an co-array of shape [10] and the corresponding dummy argument is a co-array of shape [3,3]. Again, there are missing elements. We therefore propose a rewording of the sentence. Edit to J3/07-007 [20:24+] In the note at the end of 2.4.6 Co-array, change the second sentence to "On a shared-memory machine, a co-array on an image and the corresponding co-arrays on other images could be implemented as a sequence of arrays with evenly spaced starting addresses."