On Fri, 22 Nov 2002 ok at cs.otago.ac.nz wrote:

> from preamble:
> 
> "Change Set:		Matrix-raok
> Date:			18 October 2002
> Author:			Richard A. O'Keefe

How does this compare to the very nice Matrix class in Croquet?

For those who have not seen it, here are some examples:

	"Create a new array"
	a := Matrix[3, 3] fill: #(1 2 3 4 5 6 7 8 9). 

	"Access individual elements"
	a[1,2].
	a[2,1].

	"Assign individual elements"
	a[3,1] := 42.
	a[1,3] := 21.

	"Access vectors"
	a[1]. 
	a[1,#all]. 
	a[#all,1]. 

	"Assign vectors"
	a[1] := #(-1 -2 -3). a.
	a[1,#all] := #(-3 -4 -5). a.
	a[#all,1] := #(-6 -7 -8). a.

	"Access sub-arrays"
	a[(1 to: 2),(1 to: 2)]. 
	a[(2 to: 3),(2 to: 3)].

	"Assign sub-arrays"
	a[(1 to: 2),(1 to: 2)] := Matrix[2, 2] fill: 1.
	a[(2 to: 3),(2 to: 3)] := Matrix[2, 2] fill: 2.

	a[#all,#all]. 
	a[#all].

"**** Dave''s examples ***"

	"Matrix addition"
	m1 := Matrix[3, 3] fill: #(1 2 3 4).
	m2 := Matrix[3, 3] fill: #(10 20 30).
	m3 := Matrix[3, 3] define: [:i1 :i2 | m1[i1, i2] + m2[i1, i2]].

	"Matrix Transpose"
	Matrix shape: (m3 matrixShape reverse) define:[:i1 :i2 | m3[i2, i1]].

	"Matrix Multiplication (matrix product):"
	m1 := Matrix[4, 3] fill: #(1 2 3 4 5 6 7).
	m2 := Matrix[3, 2] fill: #(10 20 30 40).
	m3 := Matrix[4, 2] define:[ :i1 : i2 | m1[i1,#all ] dot: m2[#all, i2]]. 

	"Laplace filter"
	lap := Matrix[3,3] fill: #(1 4 1 4 -20 4 1 4 1).

	image := Matrix[50,50] fill: 1.
	fImage := Matrix[50,50] define:[:i1 :i2|
		(image[(i1-1 to: i1+1), (i2-1 to: i2+1)] * lap) sum sum].

	image := Matrix[53,53] fill: 1.
	fImage := Matrix[50,50] define:[:i1 :i2|
		(i1 at i2) printString displayAt: 0 at 0.
		(image[(i1 to: i1+2), (i2 to: i2+2)] * lap) sum sum].


-- Bert