The following code example is taken from the book
The C++ Standard Library - A Tutorial and Reference, 2nd Edition
by Nicolai M. Josuttis, Addison Wesley Longman, 2012
Copyright © 2012 by Pearson Education, Inc. and Nicolai M. Josuttis
#include <iostream>
#include <valarray>
using namespace std;
// print valarray line-by-line
template <typename T>
void printValarray (const 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)])), 3);
// double the elements in the third row
va[slice(2,4,3)] = valarray<double>(va[slice(2,4,3)]) * 2.0;
printValarray (va, 3);
}