Comments on: Scalar Expansion and More

By: Loren

Loren — Wed, 02 Dec 2009 21:08:11 +0000

Per-

I recommend you send your example of what you would prefer as an enhancement request to technical support (link on the right of the page). I think it’s a good suggestion.

–Loren

By: per isakson

per isakson — Wed, 02 Dec 2009 20:55:22 +0000

I want to excecute many different functions with the same input argument. The user selects the functions interactively in a GUI. The functions are stored in a cell array, caFoo. I use this construct:

cellfun( @(foo,arg) feval(foo,arg), caFoo, caArg, … )

The cell array of argument, caArg, need to be of the same length as caFoo and can be created with repmat. However, in this case scalar expansion of caArg would have simplified the code.

/ per

By: StephenLL

StephenLL — Tue, 05 May 2009 15:04:55 +0000

You can also check out my _apply_ function at the FEX.

http://www.mathworks.com/matlabcentral/fileexchange/16467

While it doesn’t speed anything up, it makes the code somewhat cleaner. I wish the mathworks would add something like this to base MATLAB.

Stephen

By: Loren

Loren — Mon, 04 May 2009 11:23:57 +0000

Everett-

Many MATLAB functions already work on columns of an array or can work on a selected dimension (see help for max, for example).

–Loren

By: Everett

Everett — Sun, 03 May 2009 15:17:29 +0000

Hi, Loren,

How to apply a function to each row of a matrix with out using the for loop?

Thanks,
Everett

By: Loren

Loren — Tue, 18 Nov 2008 18:08:49 +0000

Tom-

See the function bsxfun for other scalar expansion functionality.

–Loren

By: Tom Clark

Tom Clark — Tue, 18 Nov 2008 18:04:59 +0000

Loren,

Ah ha! I can’t believe I’ve been using MATLAB in anger, daily, for years now – and hadn’t figured out the outer product.

God bless you, this just saved me 586,000 seconds… And then the rest!

Tom

By: Melchi

Melchi — Wed, 09 Apr 2008 23:36:19 +0000

Regarding “How to Add [or multiply] Constant Values to Each Column of a Matrix.” This bothered me for a long time. I used to use what Loren calls “Tony’s Method” (both versions) for a while but got frustrated with it because of the performance hit for large matrices. Though I found the repmat method to be faster than looping, I couldn’t get over the fact that I was doing so many extra additions (or multiplications). Finally, I wrote a few mex functions (e.g., rowmult(cVec,Matrix), colmult(rVec,Matrix), etc.) that calculate these directly. These are really basic operations that I use so often that I’m really shocked that they aren’t built in to Matlab. While it might be nice to eventually come up with some operators to represent these functions, I think it’s more important that efficient functions implementing these operations be included even if only in functional form.

By: Loren

Loren — Thu, 24 Jan 2008 12:22:25 +0000

Peter-

I don’t know what you are trying to calculate. Are the columns year, month, and number. You’d probably be best off reshaping your array into a 3-dimensional array and summing along the correct dimension(s) then.

–Loren

By: Peter Maclean

Peter Maclean — Wed, 23 Jan 2008 22:10:16 +0000

How to calculate a cummulative sum of a matrix over over a given varible. Example, how I calculate year totals from monthly total. The data set look like

Country month Temp
1 1 10
. . .
1 12 12
2 1 60
. . .
2 12 72