Re: arbitrary dimension array for math

From:

"Dimitri Ognibene" <dimitri.ognibene@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

8 Aug 2006 03:48:31 -0700

Message-ID:

<1155034111.840578.191840@p79g2000cwp.googlegroups.com>

thanks stefan,
I'm know very few of reflection, I used it years ago only for oo-db
mapping...
Do you know if there are any perfomance issues?
here is my simple constructor, still writing subblock extraction:
public MultiDimensionalMatrix(int[] _dimension) {
        dimensions=_dimension;
        strides=new int[dimensions.length];
        strides[dimensions.length-1]=1;
        for (int i = 0; i < dimensions.length-1; i++)
            strides[dimensions.length-2-i]=

strides[dimensions.length-1-i]*dimensions[dimensions.length-1-i];
        flatDimension=strides[0]*dimensions[0];

        flatData=new double[flatDimension];
    }

public final int[] getCoordinates(final int point_index,int result[]) {
        if (result==null)result=new int[dimensions.length];

        for (int j = 0; j < strides.length; j++) {
            result [j]=((point_index/strides[j])%dimensions[j]);
        }

        return result;
    }

.....
....
thanks very *1000 much
Dimitri
Using strides i could be able to implement the various operation, i
think, but long time has gone from my math programming courses..
for some kind of operation the structure can be easily reconstructed by
the alg... i think..
any tip?
Do you think reflection is the right way to go?
thanks

Stefan Ram wrote:

"Dimitri Ognibene" <dimitri.ognibene@gmail.com> writes:

I'm writing the code but it is rather complicated, and so it's cool,
but it could be useful to have some example.

  I wrote the following code as an example to show how to
  dynamically create and fill an arrays whose arbitrary
  extensions and arbitrary dimension is only known at run-time.

  Here it is suppossed to have 3 dimensions with extensions 4,
  5, and 6, respectively.

public class Main
{
  public static int[] cdr( final int[] list )
  { return java.util.Arrays.copyOfRange( list, 1, list.length ); }

  public static java.lang.Object build( final int ... extensions )
  { final java.lang.Object array = java.lang.reflect.Array.newInstance
    ( java.lang.Integer.TYPE, extensions );
    for( int i = 0; i < extensions[ 0 ]; ++i )if( extensions.length > 1 )
    java.lang.reflect.Array.set( array, i, build( cdr( extensions )));
    else java.lang.reflect.Array.setInt(( int[] )array, i, i );
    return array; }

  public static void print( final java.lang.Object array )
  { for( int i = 0; i < java.lang.reflect.Array.getLength( array ); ++i )
    if( array.getClass().getName().startsWith( "[[" ))
    print( java.lang.reflect.Array.get( array, i )); else
    java.lang.System.out.print( java.lang.reflect.Array.getInt( array, i )); }

  public static void main( final java.lang.String[] args )
  { print( build( 4, 5, 6 )); }}

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