Mega Code Archive
Valarray slice
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/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <valarray>
using namespace std;
// print valarray line-by-line
template<class T>
void printValarray (const valarray<T>& va, int num)
{
for (int i=0; i<va.size()/num; ++i) {
for (int j=0; j<num; ++j) {
cout << va[i*num+j] << ' ';
}
cout << endl;
}
cout << endl;
}
int main()
{
/* valarray with 12 elements
* - four rows
* - three columns
*/
valarray<double> va(12);
// fill valarray with values
for (int i=0; i<12; i++) {
va[i] = i;
}
printValarray (va, 3);
// first column = second column raised to the third column
va[slice(0,4,3)] = pow (valarray<double>(va[slice(1,4,3)]),
valarray<double>(va[slice(2,4,3)]));
printValarray (va, 3);
// create valarray with three times the third element of va
valarray<double> vb(va[slice(2,4,0)]);
// multiply the third column by the elements of vb
va[slice(2,4,3)] *= vb;
printValarray (va, 3);
// print the square root of the elements in the second row
printValarray (sqrt(valarray<double>(va[slice(3,3,1)])));
// double the elements in the third row
va[slice(2,4,3)] = valarray<double>(va[slice(2,4,3)]) * 2.0;
printValarray (va, 3);
}
/*
0 1 2
3 4 5
6 7 8
9 10 11
1 1 2
1024 4 5
5.7648e+006 7 8
1e+011 10 11
1 1 4
1024 4 10
5.7648e+006 7 16
1e+011 10 22
1 1 8
1024 4 20
5.7648e+006 7 32
1e+011 10 44
*/
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