I can give a couple other examples of matrices in java using 0 to n-1.
Colt: http://dsd.lbl.gov/~hoschek/colt/api/cern/colt/matrix/DoubleMatrix2D.html
A matrix has a number of rows and columns, which are assigned upon instance construction - The matrix's size is then rows()*columns(). Elements are accessed via [row,column] coordinates. Legal coordinates
range from [0,0] to [rows()-1,columns()-1]. Any attempt to access an
element at a coordinate column<0 || column>=columns() || row<0 || row>=rows() will throw an IndexOutOfBoundsException.
Ninja:
0 <= index[i] < size(i)
Most importantly, the JSR 83 for Multiarray is indexed in this manner:
JSR 83: http://jcp.org/en/jsr/detail?id=83
Elements of a multiarray are identified by their indices along each axis. Let a d-dimensional array A of elemental type T have extent nj along its j-th axis, j = 0,...,d-1. Then, a valid index ij along the j-th axis must be greater than or equal to zero and less than nj. An attempt to reference an element A[i0,i1,...,id-1] with any invalid index ij causes an ArrayIndexOutOfBoundsException to be thrown.
I would agree with Kim because I feel that the implementation language should dictate the indexing strategy, not mathematical notation. It makes integrating the package other API's more consistent and easier for the user to implement.
-Mark
Kim van der Linde wrote:
Hi Phil,
With the 1 base system, I keep casting back and forth between the 0 based underlying java system and the 1 based matrix system. But only in selected cases, not as a general rule. It also requires me to make
specific methods just to increase the row number by one, as the method returns them at the 0 based system. This happens always as soon as you use a matrix or array by itsself and with matrcies combined, as I do. The fact that java uses the "0-based" notation anyways conflicts with the mathematical notation.... Why not stay with that....???
As most methods in the RealMatrixImpl return a RealMatrix and NOT a RealMatrixImpl, the methods need to be in the RealMAtrix itself also.
There is no option to create a RealMatrixImpl directly from a RealMatrix, and requires casting around with new RealMatrixImpl(RealMAtrix.getArray()); MatrixUtil depends on how... But results in a lot of cating around also unless implemented as static's....
Kim
Phil Steitz wrote:
I need to understand better exactly what the problem is with the indexing. I don't see anything wrong with the current implementation. The element accessor methods use standard matrix notation, which starts with index = 1 in each case. The methods that provide access to copies of the underlying double[][] arrays are for efficiency and return arrays which are correctly sized to hold the matrix data. I would be -1 to changing the matrix accessor methods (getEntry, setEntry, getRow, getColumn) to be "0-based" as this conflicts with standard mathematical notation.
I am OK with adding the additional methods above to (post 1.0) RealMatrixImpl or a MatrixUtils class.
Phil
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