The method I used below is to separate the parts the array you want to test from the rest of the array. As you can see in the disp, the result is indeed r=[1,2,1,1] c=[1,2,1,2] v=[1,1,2,2].
B=cat(3,[2,8;0,5],[1,3;7,9]);
b=2.9;
[v,c]=meshgrid(1:size(B,3),1:size(B,2));
temp=mat2cell(B,size(B,1),ones(1,size(B,2)),ones(1,size(B,3)));
[~,row_index]=cellfun(@(x) min(abs(x-b)),temp,'uni',0);
r=cell2mat(row_index(:))';
c=c(:)';
v=v(:)';
disp([r;c;v])
