Problem in working with ismembertol

Hi everyone,

I have a question regarding matching numbers. My text file contains a column vector and I want to match the values in this column vector with the values that are stored in a variable in matrix form.

a = 29.8220 %(one value extracted from column vector of txt file); 3798x1 double
b = 2030x1354 double %(it contains interpolated values (in the form of floating point numbers), 
% actual values were '406x270');
mask = ismembertol(a,b); %answer = 1 (means true)

problem is b not only contains 29.2880, but also "29.8219, 29.8221". I tried to look for the indices of this number and I've checked that it gave me indices of 29.8219 as well as 29.8221 along with 29.8220. For example row 1192 and column 42 returns 29.8219 and row 1231 and column 210 gives 29.8220. Kindly tell me how to solve this issue? Thank you. A picture of values in b is shown below:

[i,j] = find(abs(b-29.8220)<1e-4)
i =

        1192
        1231
        1256
        1258
        1277
        1283
        1285
        1287
        1292
        1295
        1298
        1305
        1322
        1329
        1340
        1341
        1342
        1348
        1350
        1364
        1373
        1379
        1419
        1433
        1445
        1464
        1488


j =

          42
         210
         345
         358
         472
         509
         522
         535
         566
         585
         604
         648
         750
         790
         849
         854
         859
         890
         899
         962
         998
        1023
        1147
        1177
        1204
        1238
        1278

[Walter Roberson]

Remember when you use ismembertol() in that form, it is looking for the elements of a anywhere in b, not just in corresponding rows or corresponding columns.

Answer 1

[Cris LaPierre]

LIA = ismembertol(A,B) uses a default tolerance of 1e-6 for single-precision inputs and 1e-12 for double-precision inputs.

Try using this syntax instead:

LIA = ismembertol(A,B,tol)

a = 29.8220;
ismembertol(a,29.8219)

ans = logical
   0

ismembertol(a,29.8219,1e-4)

ans = logical
   1

[Zhou Ci]

It still gave me same result. I used this line:

% a = 3789x1 double;
% b = 2030x1354 double; 
mask = ismembertol(a, b, 1e-4);

ans
=3789x1 logical % (all are true (means 1))

[Cris LaPierre]

Try flipping a and b.

mask = ismembertol(b, a, 1e-4);

The result will be 2030x1354.

Here's a simple example.

a=29.8220*cumsum(ones(3798,1)*.001);    % 3798x1 double
b=29.8220+(rand(2030,1354)-.5)/10;      % 2030x1354 double
mask=ismembertol(b,a,1e-4);             % 2030x1354 logical
imagesc(mask)