A quick look at DAPPLE programming

To give you a quick look at what DAPPLE programs look like, let's look at a program for computing Pascal's triangle. First of all, here is Pascal's triangle:

1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1 1 7 21 35 35 21 7 1 1 8 28 56 70 56 28 8 1 1 9 36 84 126 126 84 36 9 1 1 10 45 120 210 252 210 120 45 10 1 Each row is computed from the previous row; each entry in a new row is found by adding the number above it to the number above and to the left.


Here is the beginning of a DAPPLE program to compute Pascal's triangle:

const int N = 11; intVector arow(N); This defines an integer vector called "arow", with N elements numbered 0, 1, ..., N-1. This vector will soon contain one row of the triangle, but for now the elements are uninitialized. Vectors may be initialized as part of their definition, to a scalar, an array, another vector, or a function of the index. Now we see an example of the latter: // defined by DAPPLE; returns i extern int Identity(int i); // which virtual processor am I? const intVector VP(N, Identity); This defines an N-element integer vector called "VP", initialized so that element i has value i. ifp (VP == 0) { arow = 1; cout << arow << endl; } else arow = 0; This uses the parallel if statement to initialize "arow". The "then" clause executes only for those virtual processors where the condition (VP == 0) is true, in this case, only virtual processor 0. Thus, it assigns and prints arow[0]. This one element is of course the entire first row of Pascal's triangle. The "else" clause executes for the remaining virtual processors. // to each element, add the element to the left for (int i = 1; i <= N-1; i++) { arow += shift(arow, 1); ifp (VP <= i) cout << arow << endl; } This for loop computes and prints N-1 more rows. Each time through the loop we compute a new row of the triangle, in parallel, by adding the current row to itself, shifted one to the right (a zero is shifted in at the left side). Then, we print out the vector, but only elements 0 through i, i.e., the non-zero elements of "arow". The output looks like that above.

You can see whole program, if you like.
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