Reductions
A reduction takes a vector or matrix and produces a scalar value; for
example, a sum reduction computes the sum of all values in the vector
or matrix.
DAPPLE includes many different kinds of reductions, for both vectors
and matrices:
<![CDATA[
intVector A(N);
int x;
...
x = sum(A); // x = A[0] + A[1] + ... + A[N-1]
x = any(A); // x = true iff ANY of A[i] != 0 for i in 0..N-1
x = all(A); // x = true iff ALL of A[i] != 0 for i in 0..N-1
x = n_nonzeros(A); // x = number of nonzero elements in A
x = n_active(A); // x = number of active elements in A
x = max_value(A); // x = max of A[i] for i in 0..N-1
x = min_value(A); // x = min of A[i] for i in 0..N-1
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Only the active elements contribute to the reduction. sum(),
max_value(), and min_value() do not apply to boolean vectors or
matrices.
DAPPLE includes some reductions only for vectors:
<![CDATA[
intVector A(N);
int x;
...
x = first(A); // x = A[first_index(A)]
x = first_index(A); // x = i if i is the smallest-numbered active virtual processor
x = max_index(A); // x = i if A[i] is max of A[j] for j in 0..N-1
x = min_index(A); // x = i if A[i] is min of A[j] for j in 0..N-1
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Again, only the active elements contribute to the reduction.
max_index(), and min_index() do not apply to boolean vectors.