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Control Whether a Cell Array Is Variable-Size

The code generator classifies a variable-size cell array as homogeneous. The cell array elements must have the same class. In the generated code, the cell array is represented as an array.

If a cell array is an entry-point function input, to make it variable-size, use coder.typeof or coder.newtype to create a type for a variable-size cell array. For example, to create a type for a cell array whose first dimension is fixed and whose second dimension has an upper bound of 10, use this code:

 t = coder.typeof({1 2 3}, [1 10], [0 1])

See Specify Variable-Size Cell Array Inputs.

If a cell array is not an entry-point function input, to make it variable-size:

  • Create the cell array by using the cell function. For example:

    function z = mycell(n, j)
%#codegen
x = cell(1,n);   
for i = 1:n
    x{i} = i;
end
z = x{j};
end

    For code generation, when you create a variable-size cell array by using cell, you must make sure that you assign values to all cell array elements. See Resolve Issue: Cell Array Elements Must Be Fully Defined Before Use (MATLAB Coder).

  • Grow the cell array. For example:

    function z = mycell(n)
%#codegen
c = {1 2 3};
for i = 1:n
    c{end + 1} = 1;
end
z = c{n};
end

  • Force the cell array to be variable-size by using coder.varsize. Consider this code:

    function y =  mycellfun()
%#codegen
c = {1 2 3};
coder.varsize('c', [1 10]);
y = c;
end

    Without coder.varsize, c is fixed-size with dimensions 1-by-3. With coder.varsize, c is variable-size with an upper bound of 10.

    Sometimes, using coder.varsize changes the classification of a cell array from heterogeneous to homogeneous. Consider this code:

    function y =  mycell()
%#codegen
c = {1 [2 3]};
y = c{2};
end

    The code generator classifies c as heterogeneous because the elements have different sizes. c is fixed-size with dimensions 1-by-2. If you use coder.varsize with c, it becomes homogeneous. For example:

    function y =  mycell()
%#codegen
c = {1 [2 3]};
coder.varsize('c', [1 10], [0 1]);
y = c{2};
end

    c becomes a variable-size homogeneous cell array with dimensions 1-by-:10.

    To force c to be homogeneous, but not variable-size, specify that none of the dimensions vary. For example:

    function y =  mycell()
%#codegen
c = {1 [2 3]};
coder.varsize('c', [1 2], [0 0]);
y = c{2};
end

See Also

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