3d array indexing problem

I have a 3 dimensional array with 400 pages composing the third dimension. The coordinates are (y,x,time). [x and y are flipped because of how I am displaying the resulting image afterwards]. I want to select the data contained in (Yi,Xi,:), where Yi and Xi are some numbers less than or equal to the maximum Y and X values, permute it to make it a column,and later compare its entries to those of a column extracted from a two dimensional array. When I create the "variable" three_Drow=3Dmat(Yi,Xi,:), and before I permute it,the workspace says that three_Drow is 1x1x400, type double. Comparing any possible permutation of three_Drow (400x1x1,etc) to the column from the 2D array, with dimensions 400x1, is therefore not possible. Is there any way I can work with (Yi,Xi,:) so that the comparison is possible?

[Jan]

What does "Yi and Xi are some numbers" mean exactly? Are they scalars or arrays? What do you permute? How do you compare the result? Why is "comparing not possible"? Please post the code and the error message.