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Subject: Re: Angle between two vectors
Date: Tue, 20 Jul 2010 07:54:36 -0400
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"Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in 
message news:i221e8$3du$1@fred.mathworks.com...
> "Loren_Shure" <loren.shure@mathworks.com> wrote in message 
> <i21g0k$ker$1@fred.mathworks.com>...
>> Have you checked out the function subspace: 
>> http://www.mathworks.com/access/helpdesk/help/techdoc/ref/subspace.html ?
>> -- 
>> Loren
>> http://blogs.mathworks.com/loren/
>> http://matlabwiki.mathworks.com/MATLAB_FAQ
> - - - - - - - - -
>  Yes, Loren, as Urs has said, that was discussed in article #46 of this 
> overly-long thread.  The person proposing to use subspace was seeking an 
> angle that ranges from 0 to pi (180 deg) as in the inner angle in 
> triangles, but subspace would not give an angle beyond pi/2 in this case. 
> For example
>
> a = subspace([1;0],[-1;1]) ---> 1/4*pi
>
> whereas
>
> a = acos([1;0],[-1;1]) --> 3/4*pi
>
>  This reminds me.  As I pointed out in that #46 article, Mathworks' 
> documents are still in error in claiming about subspace "If A and B are 
> column vectors of unit length, this is the same as acos(A'*B)."  This 
> error was present in my manual for system 4a back in 1994 and it still 
> persists to this day in their most recent documentation.  It should read 
> acos(abs(A'*B)).  Have you any influence with the documentation department 
> to get them to finally make a correction on this misleading statement?
>
> Roger Stafford
>

Roger-

Will enter a request to update the doc...

-- 
Loren
http://blogs.mathworks.com/loren/
http://matlabwiki.mathworks.com/MATLAB_FAQ