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finding a minimum from multiple matricies

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jenka
jenka 2012-9-17
Hi everybody, I have a few large matricies of equal size. At each location, I would like to find minimum and its index. Note, essentially an index in this case would correpsond to a particular matrix. Say I have two matricies first=[2 3 4] and second=[4 5 2] Then at location (1,1) the minimum would be 2 with index=1 as to correcpond to the first matrix. I am wondering if there is a way to do it without runing double for loop? Thanks!

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回答（5 个）

Andrei Bobrov
Andrei Bobrov 2012-9-17
Let your three matrices in 3D array M
M = randi(234,5,5,3); % initial array
[v,ii] = min(M,[],3);
Sean de Wolski
Sean de Wolski 2012-9-17
first=[2 3 4];
second=[4 5 2]
val = min(first,second);
idx = (second==val)+1
Azzi Abdelmalek
Azzi Abdelmalek 2012-9-17
编辑：Azzi Abdelmalek 2012-9-17
A={rand(4,5),rand(4,5),rand(4,5),rand(4,5)};
[c,idx1]=cellfun(@(x) min(x(:)),A)
[value,matnum]=min(c) % value = minimum and matnum= matrix number
idx=idx1(matnum)
nA=4 % nA, each matrix is nA x mA
n=mod(idx,nA)
if n==0
n==nA
end
m=ceil(idx/nA) % the location is (n,m)
Image Analyst
Image Analyst 2012-9-17
编辑：Image Analyst 2012-9-17
Here's a demo for 4 small matrices. You can adapt it for more matrices, and for larger matrices:
format compact;
m1 = rand(5,5)
m2 = rand(5,5)
m3 = rand(5,5)
m4 = rand(5,5)
% Now we have our several "large" matrixes.
% Concatenate them
m3D = cat(3, m1, m2, m3, m4);
% Find the min and a map of what matrix it occurred in.
[min2DImage matrixWhereItOccurs] = min(m3D, [], 3)
Results:
m1 =
Columns 1 through 3
0.683715572408358 0.640717922965926 0.740032327987778
0.132082955713563 0.328814214756803 0.234826914747904
0.722724539656766 0.653812022595774 0.734957541696052
0.110353480642349 0.749131463103519 0.970598525086614
0.117492852151833 0.583185731454876 0.866930291751916
Columns 4 through 5
0.0862345298634963 0.789363943641905
0.366436616319199 0.367652918437877
0.369198804330018 0.206027859505195
0.685028472661609 0.0866665473955323
0.597941635383889 0.771933917099107
m2 =
Columns 1 through 3
0.20567452146476 0.48448037239818 0.237373019705579
0.388271631047802 0.151845525116267 0.530872257027928
0.551778531957227 0.781931966588002 0.0914987313394122
0.2289532520231 0.100606322362422 0.405315419880591
0.641940620399187 0.294066333758628 0.104846247115757
Columns 4 through 5
0.112283962156027 0.432484993970361
0.784427890743913 0.69475219461794
0.291570317906931 0.758099275289454
0.603533438750887 0.432642326147101
0.964422667215901 0.655498039803537
m3 =
Columns 1 through 3
0.109755050723052 0.487603775433924 0.673294914108653
0.933759848385332 0.768958264058869 0.429564459251853
0.187460806421687 0.396006745217875 0.451739234904736
0.266178838907639 0.272938794123691 0.609857169290216
0.797830260211597 0.037234634070328 0.0594032968582772
Columns 4 through 5
0.315811438338866 0.0923523387192016
0.772722130862935 0.00782029356933489
0.696432989006095 0.423109385164167
0.12533218110918 0.655573174937914
0.130151450389424 0.722922524692024
m4 =
Columns 1 through 3
0.531209293582439 0.0985940927109977 0.316428999146291
0.108817938273045 0.142027248431928 0.217563309422821
0.631766373528489 0.168251298491528 0.251041846015736
0.126499865329303 0.196248922256955 0.892922405285977
0.134303304313575 0.317479775149435 0.703223224556291
Columns 4 through 5
0.555737942719387 0.706715217696931
0.184433667757653 0.557788966754876
0.212030842532321 0.313428989936591
0.0773468081126768 0.166203562902151
0.913800410779568 0.622497259279895
min2DImage =
Columns 1 through 3
0.109755050723052 0.0985940927109977 0.237373019705579
0.108817938273045 0.142027248431928 0.217563309422821
0.187460806421687 0.168251298491528 0.0914987313394122
0.110353480642349 0.100606322362422 0.405315419880591
0.117492852151833 0.037234634070328 0.0594032968582772
Columns 4 through 5
0.0862345298634963 0.0923523387192016
0.184433667757653 0.00782029356933489
0.212030842532321 0.206027859505195
0.0773468081126768 0.0866665473955323
0.130151450389424 0.622497259279895
matrixWhereItOccurs =
3 4 2 1 3
4 4 4 4 3
3 4 2 4 1
1 2 2 4 1
1 3 3 3 4
jenka
jenka 2012-9-18
You, guys, are soooooooooooooo great! Awesome! and thank you!

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