Re: MacOSX: Octave.app 2.9.14

[Quentin Spencer]

John W. Eaton wrote:
> On  3-Oct-2007, Quentin Spencer wrote:
>
> | John W. Eaton wrote:
> | > On 30-Sep-2007, Dmitri A. Sergatskov wrote:
> | >
> | > | Another speedup can be done if we make a norm (x,1) a special case,
> | > | so instead of calculating:
> | > | 
> | > | octave:29> tic; sum((abs(x) .^1))^1 ; toc
> | > | Elapsed time is 0.174812 seconds.
> | > | 
> | > | We can simply calculate:
> | > | 
> | > | octave:30> tic; sum((abs(x))) ; toc
> | > | Elapsed time is 0.080658 seconds.
> | >
> | > Patches, anyone?
> | >   
> | 
> | It looks like it should be as simple as this.
>
> Thanks.
>
> What about the other suggestions here:
>
>   http://www.cae.wisc.edu/pipermail/help-octave/2007-September/006001.html
>
>   

OK, here's another version with special cases for p==2 and real and 
complex inputs.

Quentin

Index: scripts/linear-algebra/norm.m
===================================================================
RCS file: /cvs/octave/scripts/linear-algebra/norm.m,v
retrieving revision 1.31
diff -u -r1.31 norm.m
--- scripts/linear-algebra/norm.m       1 Oct 2007 15:59:33 -0000       1.31
+++ scripts/linear-algebra/norm.m       3 Oct 2007 21:19:56 -0000
@@ -93,6 +93,16 @@
           retval = max (abs (x));
         elseif (p == -Inf)
           retval = min (abs (x));
+        elseif (p == 1)
+          retval = sum (abs (x));
+        elseif (p == 2)
+          if (iscomplex (x))
+            y = abs(x);
+            y .*= y;
+            retval = sqrt (sum (y));
+          else
+            retval = sqrt (sum (x .* x));
+          endif
         else
           retval = sum (abs (x) .^ p) ^ (1/p);
         endif