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std::gslice

De cppreference.com
< cpp‎ | numeric‎ | valarray

 
 
Bibliothèque Numerics
Fonctions mathématiques courantes
Virgule flottante environnement
Nombres complexes
Tableaux numériques
La génération de nombres pseudo-aléatoires
Moment de la compilation arithmétique rationnelle (C++11)
Génériques des opérations numériques
Original:
Generic numeric operations
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iota (C++11)
accumulate
inner_product
adjacent_difference
partial_sum
 
 
Defined in header <valarray>
class gslice;
std::gslice est la classe de sélection qui identifie un sous-ensemble d'indices std::valarray définies par un ensemble à plusieurs niveaux de progrès et de tailles. Objets de std::gslice type peuvent être utilisés comme des indices avec operator[] valarray à sélectionner, par exemple, les colonnes d'un tableau multidimensionnel représenté comme un valarray .
Original:
std::gslice is the selector class that identifies a subset of std::valarray indices defined by a multi-level set of strides and sizes. Objects of type std::gslice can be used as indices with valarray's operator[] to select, for example, columns of a multidimensional array represented as a valarray.
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Compte tenu de la s valeur de départ, la liste des progrès i
j
et une liste des tailles d
j
, un std::gslice construit à partir de ces valeurs sélectionne l'ensemble des indices k
j
=s+Σ
j
(i
j
d
j
)
.
Original:
Given the starting value s, a list of strides i
j
and a list of sizes d
j
, a std::gslice constructed from these values selects the set of indices k
j
=s+Σ
j
(i
j
d
j
)
.
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Par exemple, un GSlice avec 3 indice de départ, des progrès {19,4,1} et longueurs {2,4,3} génère l'ensemble suivant des indices:
Original:
For example, a gslice with starting index 3, strides {19,4,1} and lengths {2,4,3} generates the following set of indices:
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3 + 0*19 + 0*4 + 0*1 = 3,
3 + 0*19 + 0*4 + 1*1 = 4,
3 + 0*19 + 0*4 + 2*1 = 5,
3 + 0*19 + 1*4 + 0*1 = 7,
3 + 0*19 + 1*4 + 1*1 = 8,
...
3 + 1*19 + 3*4 + 2*1 = 36

Il est possible de construire des objets std::gslice qui sélectionnent certains indices plus d'une fois: si l'exemple ci-dessus utilise la {1,1,1} progrès, les indices auraient été {3, 4, 5, 4, 5, 6, ...} . Gslices Elles ne peuvent être utilisées comme arguments à la version const de std::valarray::operator[], sinon le comportement est indéfini .
Original:
It is possible to construct std::gslice objects that select some indices more than once: if the above example used the strides {1,1,1} , the indices would have been {3, 4, 5, 4, 5, 6, ...} . Such gslices may only be used as arguments to the const version of std::valarray::operator[], otherwise the behavior is undefined.
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[modifier] Fonctions membres

construit un GSlice
Original:
constructs a gslice
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(fonction membre publique)
accède au début de la GSlice
Original:
accesses the start of the gslice
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(fonction membre publique)
accède au tableau des progrès de la GSlice
Original:
accesses the array of strides of the gslice
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(fonction membre publique)
accède à l'ensemble de sizees de la GSlice
Original:
accesses the array of sizees of the gslice
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(fonction membre publique)

[modifier] Exemple

illustre l'utilisation de gslices pour répondre colonnes d'un tableau 3D
Original:
demonstrates the use of gslices to address columns of a 3D array
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#include <iostream>
#include <valarray>
void test_print(std::valarray<int>& v, int rows, int cols, int planes)
{
    for(int r=0; r<rows; ++r) {
        for(int c=0; c<cols; ++c) {
            for(int z=0; z<planes; ++z)
                std::cout << v[r*cols*planes + c*planes + z] << ' ';
            std::cout << '\n';
        }
        std::cout << '\n';
    }
}
int main()
{
    std::valarray<int> v = // 3d array: 2 x 4 x 3 elements
    { 111,112,113 , 121,122,123 , 131,132,133 , 141,142,143,
      211,212,213 , 221,222,223 , 231,232,233 , 241,242,243};
    // int ar3d[2][4][3]
    std::cout << "Initial 2x4x3 array:\n";
    test_print(v, 2, 4, 3);
 
    // update every value in the first columns of both planes
    v[std::gslice(0, {2, 4}, {4*3, 3})] = 1; // two level one strides of 12 elements
                                             // then four level two strides of 3 elements
 
    // subtract the third column from the second column in the 1st plane
    v[std::gslice(1, {1, 4}, {4*3, 3})] -= v[std::gslice(2, {1, 4}, {4*3, 3})];
 
    std::cout << "After column operations: \n";
    test_print(v, 2, 4, 3);
}

Résultat :

Initial 2x4x3 array:
111 112 113
121 122 123
131 132 133
141 142 143
 
211 212 213
221 222 223
231 232 233
241 242 243
 
After column operations:
1 -1 113
1 -1 123
1 -1 133
1 -1 143
 
1 212 213
1 222 223
1 232 233
1 242 243

[modifier] Voir aussi

get / set élément valarray, tranche, ou un masque
Original:
get/set valarray element, slice, or mask
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(fonction membre publique) [edit]
BLAS-like tranche d'un valarray: indice de départ, la longueur de foulée
Original:
BLAS-like slice of a valarray: starting index, length, stride
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(classe) [edit]
procuration d'un sous-ensemble d'un valarray après l'application d'une GSlice
Original:
proxy to a subset of a valarray after applying a gslice
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(classe générique) [edit]