[UPDATE] support negative indices for iget and iset.

README.md

@@ -215,7 +215,7 @@ __Note__: out-of-bounds row and column indices will silently fail.
 <a name="matrix-iset"></a>
 #### mat.iset( index, value )
 
-Sets a `Matrix` element located at a specified [`index`](#linear-indexing).
+Sets a `Matrix` element located at a specified [`index`](#linear-indexing). If `idx < 0`, the index refers to a position relative to the `Matrix` length, where `idx = -1` corresponds to the last element. 
 
 ``` javascript
 mat.iset( 7, 25 );
@@ -226,6 +226,15 @@ mat.iset( 7, 25 );
 	  6 25
 	  8 9 ]
 */
+
+mat.iset( -3, 20 );
+/*
+	[ 0 1
+	  2 3
+	  4 5
+	  6 20
+	  8 9 ]
+*/
 ```
 
 __Note__: out-of-bounds indices will silently fail.
@@ -344,11 +353,14 @@ __Note__: out-of-bounds row and column indices will return a value of `undefined
 <a name="matrix-iget"></a>
 #### mat.iget( index )
 
-Returns a `Matrix` element located at a specified [`index`](#linear-indexing).
+Returns a `Matrix` element located at a specified [`index`](#linear-indexing). If `idx < 0`, the index refers to a position relative to the `Matrix` length, where `idx = -1` corresponds to the last element. 
 
 ``` javascript
 var value = mat.iget( 7 );
 // returns 7
+
+value = mat.iget( -3 );
+// returns 7
 ```
 
 __Note__: out-of-bounds indices will return a value of `undefined`.

TODO.md

@@ -18,7 +18,7 @@ TODO
 5. 
 6. 
 7. 
-8. should we allow negative indices for `iset`, `iget`, etc?
+8.
 9. 
 10. pretty print a matrix
 	-	separate module? => `compute-print-matrix`

benchmark/b.iget.js

@@ -0,0 +1,56 @@
+'use strict';
+
+// MODULES //
+
+var matrix = require( './../lib' );
+
+
+// VARIABLES //
+
+var start,
+	stop,
+	nRows,
+	nCols,
+	res,
+	len,
+	m,
+	v,
+	i, j;
+
+
+// --------------------------------------
+// WARM-UP
+
+len = 1e6;
+for ( i = 0; i < len; i++ ) {
+	i = i;
+}
+
+
+// --------------------------------------
+// BENCHMARK
+
+len = 1e6;
+nRows = 128;
+nCols = 128;
+
+res = new Array( 1 );
+
+m = matrix( [nRows,nCols] );
+j = 64*m.strides[0] + 1*m.strides[1];
+
+start = process.hrtime();
+for ( i = 0; i < len; i++ ) {
+	v = m.iget( j );
+}
+stop = process.hrtime( start );
+
+res[ 0 ] = stop[ 0 ] + stop[ 1 ]*1e-9;
+
+
+// --------------------------------------
+// RESULTS
+
+console.log( 'iget:\t%d ops/sec', Math.floor( len/res[ 0 ] ) );
+console.log( '\n' );
+

lib/iget.js

@@ -9,6 +9,9 @@
 */
 function iget( idx ) {
 	/*jshint validthis:true */
+	if ( idx < 0 ) {
+		idx += this.length;
+	}
 	return this.data[ idx ];
 } // end FUNCTION iget()
 

lib/iset.js

@@ -10,6 +10,9 @@
 */
 function iset( idx, v ) {
 	/* jshint validthis: true */
+	if ( idx < 0 ) {
+		idx += this.length;
+	}
 	this.data[ idx ] = v;
 	return this;
 } // end FUNCTION iset()