Subtracting vectors from matrices

[Ryan Peterson]

Hi all, this is my first time posting to the helplist so don't lynch me if 
this is either trivial or something inappropriate for the helplist... with 
that said...

Has anyone done any work on overloading the addition or subtraction 
functions so that one might add a column vector to each column in a larger 
matrix?

Currently my sample code looks like this:

r=rand(3,3);
pnts=rand(3,100000);
tic;
rotpnts=r*pnts;
###method 1
diffx=rotpnts(1,:)-rotpnts(1,1);
diffy=rotpnts(2,:)-rotpnts(2,1);
diffz=rotpnts(3,:)-rotpnts(3,1);
###method 2 - for a taste of what the speed could be.
# diff=rotpnts-rotpnts(1,1);
toc

I would have guessed that the major time cost would have been in the matrix 
multiplication,
but 1 run of it shows the subtraction routines take more than ten times 
longer to run than the matrix in multiplication (in method 1).  Just 
subtracting a scalar (as in method 2) takes around 1/4th as long as the 
matrix multiplication (~40X faster overall).  It would be nice if something 
like
diff=rotpnts-rotpnts(1:3,1) would work in some way (maybe through a special 
function call).  Does anyone have experience with this?

I realize there are probably other ways to do what I'm ultimately exploring 
for my own amusement, but this seems like a feature that might be useful to 
others?

Any suggestions?

Thanks in advance,
Ryan Peterson




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