Programming and Data Types

Operating on Planes and Matrices

Functions that operate on planes or matrices, such as the linear algebra and matrix functions in the matfun directory, do not accept multidimensional arrays as arguments. That is, you cannot use the functions in the matfun directory, or the array operators *, ^, \, or /, with multidimensional arguments. Supplying multidimensional arguments or operands in these cases results in an error.

You can use indexing to apply a matrix function or operator to matrices within a multidimensional array. For example, create a three-dimensional array A

• A = cat(3,[1 2 3;9 8 7;4 6 5],[0 3 2;8 8 4;5 3 5],[6 4 7;6 8 5;...
  5 4 3]);
  

Applying the eig function to the entire multidimensional array results in an error.

• eig(A)
  ??? Error using ==> eig
  Input arguments must be 2-D.
  

You can, however, apply eig to planes within the array. For example, use colon notation to index just one page (in this case, the second) of the array.

• eig(A(:,:,2))
  ans =
     -2.6260
     12.9129
      2.7131
  

Note    In the first case, subscripts are not colons, you must use squeeze to avoid an error. For example, eig(A(2,:,:)) results in an error because the size of the input is [1 3 3]. The expression eig(squeeze(A(2,:,:))), however, passes a valid two-dimensional matrix to eig.

Computing with Multidimensional Arrays

Organizing Data in Multidimensional Arrays