How to find the position of a real vector in a matrix?

I do have a very big matrix of real numbers, I need a function that takes a vector as input and returns its position in the matrix.

An example:

A =[
    0.7081    0.0797    0.1418    0.5849    0.1305
    0.0738    0.4849    0.5060    0.8479    0.5003
    0.8723    0.1511    0.6346    0.0683    0.7673
    0.2021    0.4461    0.7313    0.7355    0.4157
    0.7050    0.8435    0.8158    0.2139    0.8008]

Suppose I want to find the position of

v=[  0.7081    0.0797    0.1418    0.5849    0.1305] 

in A

How can I do it?

I edited the question

[Walter Roberson]

You cannot. Those values do not exist in the matrix.

You need to give the command

format long g

And then display A again.

[Cantor Set]

Sorry, I edited the question

Answer 1

[dpb]

>> find(ismember(A,v,'rows'))
ans =
     1
>> 

works here, but in general for floating point values

>> find(ismembertol(A,v,2*eps,'byrows',1))
ans =
     1
>> 

is more robust and will avoid surprises.

[Cantor Set]

I tried it on a very big matrix of real numbers it returned

ans =

Empty matrix: 0-by-1

[dpb]

>> find(ismembertol(w,c,2*eps,'byrows',1))
ans =
     1
>> 

Answer 2

[Walter Roberson]

Dists = pdist2(A, v);
[mindist, rowidx] = min(Dists) ;
if mindist > some_tolerance
  error('row not found') ;
end

[Cantor Set]

w =[
  472.1745  237.0587  217.2062
  482.5531  230.1160  214.5375
  511.5849  221.5821  203.8826
  528.9620  210.4759  200.9207
  550.9417  196.1739  193.1201
  559.0008  207.2335  186.1113
  579.9176  188.3211  185.3489
  600.6789  178.9065  181.5854
  602.5532  159.9476  178.6138
  610.0186  163.3685  171.5659
  627.4484  155.7319  176.9325
  632.2046  152.3424  175.2902
  637.9136  182.4038  149.4447
  653.2446  145.8217  169.4935
  653.4360  145.6781  169.4251
  653.6974  145.5827  169.3469
  654.4806  145.2974  169.1123
  654.7265  155.4882  168.9364
  655.5309  155.2029  168.7018
  655.7820  144.8259  168.7213
  657.4487  168.3275  149.6988
  657.9721  142.2886  167.7829
  658.2313  142.1932  167.7047
  658.5682  153.4142  163.8239
  659.0075  141.9079  167.4701
  660.2975  141.4364  167.0791
  661.7071  142.7182  166.9227
  664.5972  140.9109  165.8474
  666.1699  139.3287  165.2804
  667.4011  141.2962  165.2218
  670.1464  151.4256  163.8435
  671.8341  139.3555  163.7848
  672.0185  139.2119  163.7164
  674.3094  148.3308  161.7418
  674.6270  148.1336  161.5659
  674.8512  147.9573  161.4975
  675.4193  147.8472  161.3313
  675.6830  147.7521  161.2531
  675.9466  147.6572  161.1749
  676.3873  135.8224  162.0742
  678.8491  123.5834  142.7682
  680.1346  119.4330  154.2834
  684.0921  117.2617  152.1622
  697.7402  114.0022  151.0869
  699.3930  113.3286  150.5395
  699.6284  113.2331  150.4613
  700.3333  112.9479  150.2267
  702.9594  126.3037  141.0282
  703.0034  109.2507  146.7760
  703.1357  111.8242  149.2883
  704.6020  108.5772  146.2286
  704.8296  108.4817  146.1504
  705.2194  110.9995  148.5845
  705.5113  108.1965  145.9158
  706.6765  107.0795  144.6548
  708.2208  107.0728  144.9774
  708.2543  106.4059  144.1074
  708.4790  106.3105  144.0292
  709.1518  106.0252  143.7946
  710.2349  106.2481  144.2736
  711.8258  104.9015  142.8562
  712.4363  119.5465  136.8249
  713.8132  104.0768  142.1524
  716.8004  118.1622  134.5669
  717.6171  106.2958  144.2834
  720.0016  102.3000  141.9667
  720.2272  102.2049  141.8885
  720.2637   99.9861  136.6783
  720.4527  102.1100  141.8103
  721.1277  101.8265  141.5757
  721.2040   99.5198  135.9940
  721.6670   99.2938  135.6519
  721.7590   99.2492  135.5835
  721.8508   99.2048  135.5151
  722.2068  101.5444  139.9725
  722.5785   98.8562  134.9676
  722.7751   99.5114  128.6627
  724.8787   99.0867  126.2677
  725.6222   99.3731  137.8513
  725.8663   98.6094  125.8767
  726.0632   98.5145  125.7985
  727.1261   99.3523  139.4642
  729.0721  104.0235  142.0351
  729.2169   97.7742  138.3890
  730.5481   96.5638  124.4887
  731.5295   96.0865  124.0977
  731.7252   95.9916  124.0195
  731.9624   95.8937  123.9608
  732.1112   96.5233  137.3723
  732.3325   96.4285  137.2941
  733.1793  100.9457  138.5747
  733.5947   94.9630  122.7487
  735.1199   96.1880  136.5708
  735.6291   95.0281  136.1211
  736.2833   94.7532  135.8865
  737.0511   93.4551  123.1201
  737.5205   93.3695  122.5727
  738.0311   92.9778  122.7291
  738.2265   92.8829  122.6509
  738.4966   92.8922  122.1817
  738.6912   92.7973  122.1035
  739.2082   92.4401  120.9696
  739.5890   92.2241  122.1035
  740.0484   92.1385  121.5561
  744.2080   90.2671  131.7614
  744.4229   90.1722  131.6832
  744.8522   89.9830  131.5268
  748.7793   92.3544  130.0410];

________________________________________________

for example

c=[472.1745  237.0587  217.2062]; % which is the first row in w

when I type your code

Dists = pdist2(w, c);
[mindist, rowidx] = min(Dists) ;
if mindist > 1e-10
  error('row not found') ;
end

It tells me row not found

[dpb]

Shouldn't w/ the given example data...altho suppose it's possible with the real data instead of that rounded off in the pasted text instead of actual data from memory.

>> D=pdist2(w,c);
>> [minD,ixMin]=min(D)
minD =
     0
ixMin =
     1
>> 

With the rounded data from the posting it's identically zero.

Did you look at what was returned at all or just complain...

[Walter Roberson]

Please attach your w and c in a .mat