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From: Qianqian Fang on 25 Jul 2010 15:23
hi

I want to know if matlab support in-place operations for simple
calculations. This particular question raised when I run a vector
update with a long index:

vol(longidx)=vol(longidx)+weight*val(goodidx);

Very often, matlab complains that memory is running out. I need
something like "vol+=newadd" as in C/C++, where the memory is updated
in-place without creating a temporary variable.

does any one know if matlab is capable of doing this?

Qianqian
From: us on 25 Jul 2010 15:36
Qianqian Fang <fangqq(a)gmail.com> wrote in message <4b984d05-ba1f-4ef7-97ca-fbce6e7c6ea4(a)q35g2000yqn.googlegroups.com>...
> hi
>
> I want to know if matlab support in-place operations for simple
> calculations. This particular question raised when I run a vector
> update with a long index:
>
> vol(longidx)=vol(longidx)+weight*val(goodidx);
>
> Very often, matlab complains that memory is running out. I need
> something like "vol+=newadd" as in C/C++, where the memory is updated
> in-place without creating a temporary variable.
>
> does any one know if matlab is capable of doing this?
>
> Qianqian

this
1) has been discussed over and over in this NG (and TMW blogs)...
-and-
2) is currently not a ML feature...

consider using a MEX-file approach...

us
From: Qianqian Fang on 25 Jul 2010 16:24
On Jul 25, 3:36 pm, "us " <u...(a)neurol.unizh.ch> wrote:
> Qianqian Fang <fan...(a)gmail.com> wrote in message <4b984d05-ba1f-4ef7-97ca-fbce6e7c6...(a)q35g2000yqn.googlegroups.com>...
> > hi
>
> > I want to know if matlab support in-place operations for simple
> > calculations. This particular question raised when I run a vector
> > update with a long index:
>
> > vol(longidx)=vol(longidx)+weight*val(goodidx);
>
> > Very often, matlab complains that memory is running out. I need
> > something like "vol+=newadd" as in C/C++, where the memory is updated
> > in-place without creating a temporary variable.
>
> > does any one know if matlab is capable of doing this?
>
> > Qianqian
>
> this
> 1) has been discussed over and over in this NG (and TMW blogs)...
> -and-
> 2) is currently not a ML feature...

thanks for the quick response. Before I post my question, I did search
this list with
some keywords, but nothing came up relevant:

http://groups.google.com/group/comp.soft-sys.matlab/search?group=comp.soft-sys.matlab&q=+in-place+operations&qt_g=Search+this+group

anyway. I am going to give up now and use loop to reduce memory
utility.


Qianqian

>
> consider using a MEX-file approach...
>
> us

From: Matt J on 25 Jul 2010 18:23
Qianqian Fang <fangqq(a)gmail.com> wrote in message <4b984d05-ba1f-4ef7-97ca-fbce6e7c6ea4(a)q35g2000yqn.googlegroups.com>...
> hi
>
> I want to know if matlab support in-place operations for simple
> calculations. This particular question raised when I run a vector
> update with a long index:
>
> vol(longidx)=vol(longidx)+weight*val(goodidx);
>
> Very often, matlab complains that memory is running out. I need
> something like "vol+=newadd" as in C/C++, where the memory is updated
> in-place without creating a temporary variable.
==============

In-place processing happens for operations that make element-wise changes to an existing array, like the one you've shown. You can verify this with some simple experiments like below:

clear V; V=rand(500,500,330); %a big array

>> A=V+1;
??? Out of memory. Type HELP MEMORY for your options.

>> V=V+1; %No error
From: Jan Simon on 25 Jul 2010 18:45
Dear Qianqian,

> I want to know if matlab support in-place operations for simple
> calculations.
> vol(longidx)=vol(longidx)+weight*val(goodidx);

Matlab 2009a, WinXP, 32 bit:
format debug
x = rand(1000, 1);
x(1)
>> structure address = a820940
>> pr = bb51b80 (pointer to the real double array)

v = rand(1000, 1) < 0.2;
x(v) = x(v) + rand(sum(v), 1);
x(1)
>> structure address = a820940
>> pr = bb51b80

So it looks, like Matlab *does* inplace operations even *without* the += operator.

Good luck, Jan
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