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In a scan of a vector, each element of the result is a function of the elements of the vector that precede it (for a prefix scan) or that follow it (for a suffix scan). These functions provide scan operations on arrays and subarrays. The functions have the general form
XXX_PREFIX(ARRAY, DIM, MASK, SEGMENT, EXCLUSIVE) XXX_SUFFIX(ARRAY, DIM, MASK, SEGMENT, EXCLUSIVE)
except in the special cases noted below. The allowed values of XXX are ALL, ANY, COPY, COUNT, IALL, IANY, IPARITY, MAXVAL, MINVAL, PARITY, PRODUCT, and SUM.
When comments below apply to both prefix and suffix forms of the routines, we will refer to them as YYYFIX functions.
The arguments DIM, MASK, SEGMENT, and EXCLUSIVE are optional. The COPY_YYYFIX functions do not have MASK or EXCLUSIVE arguments. The ALL_YYYFIX, ANY_YYYFIX, COUNT_YYYFIX, and PARITY_YYYFIX functions do not have MASK arguments. Their ARRAY argument must be of type logical; it is denoted MASK in their specifications in Section 7.7.
The arguments MASK and SEGMENT must be of type logical. SEGMENT must have the same shape as ARRAY. MASK must be conformable with ARRAY. EXCLUSIVE is a logical scalar. DIM is a scalar integer between one and the rank of ARRAY.
In every case, every element of the result is determined by the values of certain selected elements of ARRAY in a way that is specific to the particular function and is described in its specification. The optional arguments affect the selection of elements of ARRAY for each element of the result; the selected elements of ARRAY are said to contribute to the result element. This section describes fully which elements of ARRAY contribute to a given element of the result.
If no elements of ARRAY are selected for a given element of the result, that result element is set to a default value that is specific to the particular function and is described in its specification.
For any given element r of the result, let a be the corresponding element of ARRAY. Every element of ARRAY contributes to r unless disqualified by one of the following rules.
These general rules lead to the following important cases:
Case (i): If ARRAY has rank one, element i of the result of XXX_PREFIX(ARRAY) is determined by the first i elements of ARRAY; element SIZE(ARRAY)-i+1 of the result of XXX_SUFFIX(ARRAY) is determined by the last i elements of ARRAY.
Case (ii): If ARRAY has rank greater than one, then each element of the result of XXX_PREFIX(ARRAY) has a value determined by the corresponding element of the ARRAY and all elements of ARRAY that precede a in array element order. For XXX_SUFFIX, a is determined by the elements of ARRAY that correspond to or follow a in array element order.
Case (iii): Each element of the result of XXX_PREFIX(ARRAY,MASK=MASK) is determined by selected elements of ARRAY, namely the corresponding element of the ARRAY and all elements of ARRAY that precede in array element order, but an element of ARRAY may contribute to the result only if the corresponding element of MASK is true. If this restriction results in selecting no array elements to contribute to some element of the result, then that element of the result is set to the default value for the given function.
Case (iv): Each element of the result of XXX_PREFIX(ARRAY,DIM=DIM) is determined by selected elements of ARRAY, namely the corresponding element of the ARRAY and all elements of ARRAY that precede along dimension DIM; for example, in SUM_PREFIX(A(1:N,1:N), DIM=2), result element (i1, i2) could be computed as SUM(A(i1,1 : i2)). More generally, in SUM_PREFIX(ARRAY, DIM), result element i1, i2,...,iDIM,...,in could be computed as SUM(ARRAY( i1, i2,...,iDIM,...,in )) . (Note the colon before i_DIM in that last expression.)
Case (v): If ARRAY has rank one, then element of the result of XXX_PREFIX(ARRAY, EXCLUSIVE=.TRUE.) is determined by the first i-1 elements of ARRAY.
Case (vi): The options may be used in any combination.
(/T,T,T,F,T,F,F,F,T,F,F,T/) ----- - - ----- - --- - seven segments
(End of advice to users.)
SUM_PREFIX(FOO,SEGMENT=PARITY_PREFIX(START_BITS)) SUM_PREFIX(FOO,SEGMENT=PARITY_SUFFIX(STOP_BITS)) SUM_SUFFIX(FOO,SEGMENT=PARITY_SUFFIX(START_BITS)) SUM_SUFFIX(FOO,SEGMENT=PARITY_PREFIX(STOP_BITS))
Examples. The examples below illustrate all possible combinations of optional arguments for SUM_PREFIX. The default value for SUM_YYYFIX is zero.
Case (i): SUM_PREFIX((/1,3,5,7/)) is [1 4 9 16].
Case (ii):
/ \ | 1 2 3 | If B is the array | 4 5 6 |, | 7 8 9 | \ / / \ | 1 14 30 | then SUM_PREFIX(B) is the array | 5 19 36 |. | 12 27 45 | \ /
Case (iii): If A is the array [3 5 -2 -1 7 4 8], then SUM_PREFIX(A, MASK = A .LT. 6) is [3 8 6 5 5 9 9]
Case (iv):
/ \ | 1 2 3 | If B is the array | 4 5 6 |, | 7 8 9 | \ / / \ | 1 2 3 | then SUM_PREFIX(B, DIM=1) is the array | 5 7 9 |. | 12 15 18 | \ / / \ | 1 3 6 | and SUM_PREFIX(B, DIM=2) is the array | 4 9 15 |. | 7 15 24 | \ /
Case (v): SUM_PREFIX((/1,3,5,7/), EXCLUSIVE=.TRUE.) is [0 1 4 9].
Case (vi):
/ \ | 1 2 3 4 5 | If B is the array | 6 7 8 9 10 |, M is the array | 11 12 13 14 15 | \ / / \ / \ | T T T T T | | T T F F F | | F F T T T |, and S is the array | F T T F F |, then: | T F T F F | | T T T T T | \ / \ / SUM_PREFIX(B, DIM=2, MASK=M, SEGMENT=S, EXCLUSIVE=.TRUE.) is / \ | 0 1 0 3 7 | | 0 0 0 0 9 |. | 0 11 11 24 24 | \ / SUM_PREFIX(B, DIM=2, MASK=M, SEGMENT=S, EXCLUSIVE=.FALSE.) is / \ | 1 3 3 7 12 | | 0 0 8 9 19 |. | 11 11 24 24 24 | \ / / \ | 0 1 3 6 10 | SUM_PREFIX(B, DIM=2, MASK=M, EXCLUSIVE=.TRUE.) is | 0 0 0 8 17 |. | 0 11 11 24 24 | \ / / \ | 1 3 6 10 15 | SUM_PREFIX(B, DIM=2, MASK=M, EXCLUSIVE=.FALSE.) is | 0 0 8 17 27 |. | 11 11 24 24 24 | \ / / \ | 0 1 0 3 7 | SUM_PREFIX(B, DIM=2, SEGMENT=S, EXCLUSIVE=.TRUE.) is | 0 0 7 0 9 |. | 0 11 23 36 50 | \ / / \ | 1 3 3 7 12 | SUM_PREFIX(B, DIM=2, SEGMENT=S, EXCLUSIVE=.FALSE.) is | 6 7 15 9 19 |. | 11 23 36 50 65 | \ / / \ | 0 1 3 6 10 | SUM_PREFIX(B, DIM=2, EXCLUSIVE=.TRUE.) is | 0 6 13 21 30 |. | 0 11 23 36 50 | \ / / \ | 1 3 6 10 15 | SUM_PREFIX(B, DIM=2, EXCLUSIVE=.FALSE.) is | 6 13 21 30 40 |. | 11 23 36 50 65 | \ / / \ | 0 11 0 0 0 | SUM_PREFIX(B, MASK=M, SEGMENT=S, EXCLUSIVE=.TRUE.) is | 0 13 0 4 5 |. | 0 13 8 0 0 | \ / SUM_PREFIX(B, MASK=M, SEGMENT=S, EXCLUSIVE=.FALSE.) is / \ | 1 13 3 4 5 | | 0 13 8 13 15 |. | 11 13 21 0 0 | \ / / \ | 0 12 14 38 51 | SUM_PREFIX(B, MASK=M, EXCLUSIVE=.TRUE.) is | 1 14 17 42 66 |. | 1 14 25 51 66 | \ / / \ | 1 14 17 42 56 | SUM_PREFIX(B, MASK=M, EXCLUSIVE=.FALSE.) is | 1 14 25 51 66 |. | 12 14 38 51 66 | \ / / \ | 0 11 0 0 0 | SUM_PREFIX(B, SEGMENT=S, EXCLUSIVE=.TRUE.) is | 0 13 0 4 5 |. | 0 20 8 0 0 | \ / / \ | 1 13 3 4 5 | SUM_PREFIX(B, SEGMENT=S, EXCLUSIVE=.FALSE.) is | 6 20 8 13 15 |. | 11 32 21 14 15 | \ / / \ | 0 18 39 63 90 | SUM_PREFIX(B, EXCLUSIVE=.TRUE.) is | 1 20 42 67 95 | | 7 27 50 76 105 | \ / / \ | 0 18 39 63 90 | SUM_PREFIX(B, EXCLUSIVE=.FALSE.) is | 1 20 42 67 95 | | 18 39 63 90 120 | \ /
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