reduce.cpp

A C++ class library for scientific computing

/*****************************************************************************
 * reduce.cpp     Blitz++ array reduction example
 *
 * This example illustrates the array reduction functions provided by
 * Blitz++.  These functions reduce an N dimensional array (or array
 * expression) to an N-1 dimensional array expression by summing, taking
 * the mean, etc.  These array reductions are currently provided: sum,
 * mean, min, max, minIndex, maxIndex, product, count, any and all.
 *****************************************************************************/

#include <blitz/array.h>

BZ_USING_NAMESPACE(blitz)

int main()
{
    Array<int, 2> A(4,4);

    A = 3,  1,  2,  4,       
        8, -1, -5,  3,       
        0,  9, -1,  4,
        1,  3,  1,  2;

    cout << "A = " << A << endl;

    /*
     * Reduce the array A to a one-dimensional array, by summing/taking
     * the mean/etc. of each row.
     */

    Array<int, 1> z(4);
    Array<float, 1> z2(4);
    secondIndex j;

    z = sum(A, j);
    cout << "sum(A,j) = " << endl << z << endl;

    z2 = mean(A, j);
    cout << "mean(A,j) = " << endl << z2 << endl;

    z = min(A, j);
    cout << "min(A,j) = " << endl << z << endl;

    z = minIndex(A, j);
    cout << "minIndex(A, j) = " << endl << z << endl;

    z = max(A, j);
    cout << "max(A, j) = " << endl << z << endl;

    z = maxIndex(A, j);
    cout << "maxIndex(A, j) = " << endl << z << endl;

    z = first((A < 0), j);
    cout << "first((A < 0), j) = " << endl << z << endl;

    z = product(A, j);
    cout << "product(A, j) = " << endl << z << endl;

    z = count( (A > 0), j);
    cout << "count((A > 0), j) = " << endl << z << endl;

    z = any((abs(A) > 4), j);
    cout << "any((abs(A) > 4), j) = " << endl << z << endl;

    z = all(A > 0, j);
    cout << "all(A > 0, j) = " << endl << z << endl;

    return 0;
}


/*
 * Output
 */
#if 0
A = 4 x 4
         3         1         2         4
         8        -1        -5         3
         0         9        -1         4
         1         3         1         2

sum(A,j) =
[         10         5        12         7 ]
mean(A,j) =
[        2.5      1.25         3      1.75 ]
min(A,j) =
[          1        -5        -1         1 ]
minIndex(A, j) =
[          1         2         2         0 ]
max(A, j) =
[          4         8         9         3 ]
maxIndex(A, j) =
[          3         0         1         1 ]
product(A, j) =
[         24       120         0         6 ]
count((A > 0), j) =
[          4         2         2         4 ]
any((abs(A) > 4), j) =
[          0         1         1         0 ]
all(A > 0, j) =
[          1         0         0         1 ]

#endif