[Jython-users] Using JAMA arrays with Jython. Jython examples

[Alfonso R. <ms...@re...>]

I was feeling the need to exercise my rusty array learnings from the
university when we used to do this with Pascal and Fortran and decided to
evaluate the Java array libraries available. One of them is JAMA, a very
powerful and simple to use matrix manipulation package.
 I chose Jython instead of Java (read also Python) because Jython is fun to
use and  don't need to declare "everything" to perform simple operations -
it is a roll-your-sleeves kind of language. Don't misunderstand me, you have
to know Java if want the get the best juice out of all.

Though I didn't ported the Jama ( http://math.nist.gov/javanumerics/jama/
http://math.nist.gov/javanumerics/jama/ ) example for speed racing purposes
(Jython vs Java), for those interested below are my results. Try it at
home=).


Jython      0.407 s

Java         0.203 s


Unless for me, Jython is not about speed, it's about fast development and
prototyping.

The Jython code here:

""" MagicSquareExample.py
Written by NIST for Jama (Java Matrix) test.
http://math.nist.gov/javanumerics/jama/
Ported to Jython by:  Alfonso Reyes, September 2007

"""
from java.util import Date;
from java.lang import Math

from Jama import *;        # Jama linear matrix library
from java.lang.reflect import Array    # will allow craeting java arrays
import java

class magic(object):

    def __new__(cls, n=5):
        """    the __new__ static method is called before __init__
            and can return a value while __init__ can't.
            cls: it's the class as 1st argument
            n: is the size of the square matrix
            Returns: a new instance of the class or object
        """
        # Not, let's create a Java array instance, two-dimensions
        # it could be more if you want.
        M = Array.newInstance(java.lang.Double.TYPE, [n,n] )

        # Odd order
        if ((n % 2) == 1):
            a = (n+1)/2;
            b = (n+1);

            for j in range(0,n,1):
                for i in range(0,n,1):
                    M[i][j] = n*((i+j+a) % n) + ((i+2*j+b) % n) + 1;

        # Doubly Even Order
        elif ((n % 4) == 0):

            for j in range(0,n,1):
                for i in range(0,n,1):
                    if (((i+1)/2)%2 == ((j+1)/2)%2):
                        M[i][j] = n*n-n*i-j;
                    else:
                        M[i][j] = n*i+j+1;

        # Singly Even Order
        else:
            p = n/2;
            k = (n-2)/4;
            A = magic(p);
            for j in range(0,p,1):
                for i in range(0,p,1):
                    aij = A.get(i,j);
                    M[i][j] = aij;
                    M[i][j+p] = aij + 2*p*p;
                    M[i+p][j] = aij + 3*p*p;
                    M[i+p][j+p] = aij + p*p;

            for i in range(0,p,1):
                for j in range(0,k,1):
                    t = M[i][j]; M[i][j] = M[i+p][j]; M[i+p][j] = t;
                for j in range(n-k+1,n,1):
                    t = M[i][j];
                    M[i][j] = M[i+p][j];
                    M[i+p][j] = t;

            t = M[k][0]; M[k][0] = M[k+p][0]; M[k+p][0] = t;
            t = M[k][k]; M[k][k] = M[k+p][k]; M[k+p][k] = t;

        return Matrix(M)        # return a Jama java matrix


def fixedWidthDoubletoString(x, w, d):
    fmt = java.text.DecimalFormat();
    fmt.setMaximumFractionDigits(d);
    fmt.setMinimumFractionDigits(d);
    fmt.setGroupingUsed(False);
    s = fmt.format(x);
    while (len(s) < w):
        s = " " + s;
    return s;


def fixedWidthIntegertoString(n, w):
    s = str(n)    #Integer.toString(n);
    while (len(s) < w):
         s = " " + s;
    return s;


if __name__ == '__main__':
    print "Testing first the nice print method of Matrix"
    M = magic(5);    # test first this nice Jama print method
    M.print(6,3)

    print "\n    Test of Matrix Class, using magic squares.\n",
    print "    See MagicSquareExample.main() for an explanation.\n",
    print "\n      n     trace       max_eig   rank        cond      lu_res     
qr_res\n\n",

    start_time = Date();
    eps = Math.pow(2.0,-52.0);
    for n in range(3,32+1,1):
        print fixedWidthIntegertoString(n,7),
        M = magic(n)

        t = int(M.trace())
        print fixedWidthIntegertoString(t,10),

        E = EigenvalueDecomposition(M.plus(M.transpose()).times(0.5));
        d = E.getRealEigenvalues();
        print fixedWidthDoubletoString(d[n-1],14,3),

        r = M.rank();
        print fixedWidthIntegertoString(r,7),

        c = M.cond();
        if (c < 1/eps ): print fixedWidthDoubletoString(c,12,3),
        else: print "         Inf",

        LU = LUDecomposition(M);
        L = LU.getL();

        U = LU.getU();

        p = LU.getPivot();

        R = L.times(U).minus(M.getMatrix(p,0,n-1));

        res = R.norm1()/(n*eps);
        print fixedWidthDoubletoString(res,12,3),

        QR = QRDecomposition(M);

        Q = QR.getQ();

        R = QR.getR();

        R = Q.times(R).minus(M);

        res = R.norm1()/(n*eps);
        print fixedWidthDoubletoString(res,12,3),

        print "\n",

    stop_time = Date();
    etime = (stop_time.getTime() - start_time.getTime())/1000.;
    print "\nElapsed Time = " , fixedWidthDoubletoString(etime,12,3), "
seconds\n"
    print "Adios\n"



This is the Java version.

http://www.nabble.com/file/p13198679/MagicSquareExample.java
MagicSquareExample.java :

Cheers!
Alfonso Reyes
Houston, Texas
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