[ rowGrid, columnGrid ] = ndgrid( 1:size(A,1), 1:size(A,2) );
idx = sub2ind( size( B ), rowGrid, columnGrid, policy );
C = B( idx );
As far as I am aware you have to convert to linear indices to extract the data as above. I have done exactly this for something I am working on recently. There may be a more efficient way, but not that I am aware of.
I tested one or two values to check they were correct and also looking at
A( idx )
gives a good confidence level too since these numbers are obviously all towards the higher end of the 0-1 range, e.g.
>> stuff = A( idx );
>> mean( stuff(:) )
ans =
0.969286594713116
Note: This may be memory intensive though as you create two grids of size(A,1) * size(A,2) containing the row and column indices in order to be able to turn all your 3rd dimension indices into linear indices.
