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std::gslice

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< cpp‎ | numeric‎ | valarray

 
 
Numerik-Bibliothek
Gemeinsame mathematischen Funktionen
Floating-Point-Umgebung
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Numerische Arrays
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Compile-time rationale Arithmetik (C++11)
Generische numerische Operationen
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 ist der Selektor Klasse, die eine Teilmenge von std::valarray Indizes nach einer mehrstufigen Satz von Schritten und Größen definiert identifiziert. Objekte des Typs std::gslice als Indizes mit den valarray operator[] kann verwendet werden, um auszuwählen, beispielsweise Spalten einer multidimensionalen Array als valarray dargestellt .
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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Angesichts der Startwert s, eine Liste von Schritten i
j
und eine Liste von Größen d
j
wählt ein std::gslice aus diesen Werten aufgebaut des Satzes von Indizes 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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Zum Beispiel erzeugt ein GSlice mit Startindex 3 schreitet {19,4,1} und Längen {2,4,3} den folgenden Satz von Indizes:
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

Es ist möglich, Objekte, die einige std::gslice Indizes auszuwählen mehr als einmal zu konstruieren: wenn das obige Beispiel verwendet den Schritten {1,1,1} die Indizes würde {3, 4, 5, 4, 5, 6, ...} gewesen. Solche gslices darf nur als Argumente für die const-Version von std::valarray::operator[] verwendet werden, da sonst das Verhalten undefiniert ist .
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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[Bearbeiten] Member-Funktionen

konstruiert eine GSlice
Original:
constructs a gslice
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(öffentliche Elementfunktion)
greift auf den Beginn des GSlice
Original:
accesses the start of the gslice
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(öffentliche Elementfunktion)
greift auf die Reihe von Schritten der GSlice
Original:
accesses the array of strides of the gslice
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(öffentliche Elementfunktion)
greift das Array von sizees der GSlice
Original:
accesses the array of sizees of the gslice
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(öffentliche Elementfunktion)

[Bearbeiten] Beispiel

zeigt die Verwendung von gslices zum Spalten eines 3D-Feld anzusprechen
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);
}

Output:

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

[Bearbeiten] Siehe auch

get / set valarray Element, Scheibe, oder Maske
Original:
get/set valarray element, slice, or mask
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(öffentliche Elementfunktion) [edit]
BLAS-ähnliche Scheibe eines valarray: Startindex, Länge, Schritt
Original:
BLAS-like slice of a valarray: starting index, length, stride
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(Klasse) [edit]
Proxy auf eine Teilmenge eines valarray nach Anwendung eines GSlice
Original:
proxy to a subset of a valarray after applying a gslice
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(Klassen-Template) [edit]