coder.varsize

For example, create a function that defines the variable x as a 3-by-3 array, uses x by passing it to another function, and then changes the size of x depending on run-time input.

function out = changeSizeAfterUse(n) %#codegen
x = zeros(3,3);
numel(x); % use x by passing it to another function
if n < 10
    x = zeros(4,4); % change size of x depending on run-time input
end
out = x;
end

If you try to generate code for this function, the code generator produces a size mismatch error. To resolve this error, add the coder.varsize directive after you define the variable but before you use it.

function out = changeSizeAfterUse(n) %#codegen
x = zeros(3,3);
coder.varsize("x");
numel(x); % use x by passing it to another function
if n < 10
    x = zeros(4,4); % change size of x depending on run-time input
end
out = x;
end

Create a function that defines A as a scalar and then use coder.varsize to specify that A is a variable-size row vector with a maximum length of 20. Generate code for this function and examine the code generation report. A is defined as a 1x:20 array. When you do not provide the variableSize argument, non-singleton dimensions are defined as variable size and singleton dimensions remain fixed size.

function varSizeUpperBounds() %#codegen
A = 0;
coder.varsize("A",[1 20]);
end

Create a function that defines A as a 1-by-1-by-1 array and then use coder.varsize to specify that A has a first dimension that is variable-size with a maximum of 1, a second dimension with a fixed size of 3, and a third dimension that is variable-size with a maximum size of 20. Generate code for this function and examine the code generation report. A is defined as a :1x3x:20 array. The code generator defines the singleton dimension as variable size because you explicitly specified a variable-size upper bound using the upperbound and variableSize arguments.

function fcn2() %#codegen
A = [0 0 0];
coder.varsize("A",[1 3 20],[true false true]);
end

For example, create a function that defines a structure with three fields: observations1, observations2, and values. Use coder.varsize to define observations1 and observations2 as having a fixed-size first dimension and an unbounded second dimension. Use coder.varsize again to define values as a variable-size row vector with maximum length of 10. Generate code for this function and inspect the code generation report. The code generator uses internal heuristics to determine the maximum size of the unbounded dimensions of observation1 and observations2. The code generator defines observations1, observations2, and values as arrays of size 2x:10, 2x:15, and 1x:10, respectively.

function out = varSizeFields(n) %#codegen
s = struct("observations1",zeros(2,2),"observations2",zeros(2,2), ...
    "values",zeros(1,1));
coder.varsize("s.observations1","s.observations2",[2 Inf],[false true]);
coder.varsize("s.values",[1 10]);
if n <= 10
    s.observations1 = [1:n;rand(1,n)];
    s.values = randi(100,1,n);
end
if n > 0
    s.observations2 = [1:15;zeros(1,15)];
end
out = s;
end

For example, create a function that defines two 1-by-3 cell arrays, each of which contains three 1-by-2 arrays of doubles. Use coder.varsize to specify that all elements of cell array ca1 are variable-size row vectors with a maximum length of 5. Use the coder.varsize directive again to specify that the second element of ca2 is a variable-size matrix with both dimensions having a maximum size of 2. Generate code for this function and inspect the code generation report. The elements of ca1 are defined as variable-size 1x:5 arrays. The first and third elements of ca2 are defined as fixed-size 1x2 arrays, while the second element is defined as a variable-size :2x:2 matrix.

function varSizeElement %#codegen
ca1 = {[1 2] [3 4] [5 6]};
ca2 = {[1 2] [3 4] [5 6]};
coder.varsize("ca1{:}",[1 5]);
coder.varsize("ca2{2}",[2 2]);
ca1{1} = 1;
ca1{2} = 1:5;
ca1{3} = 1:3;
ca2{1} = [5 6];
ca2{2} = [1 2;3 4];
ca2{3} = [7 8];
end

For example, create a function that uses coder.varsize to declare variable x as a variable-size array two-dimensional array and sets upper bounds of 5 for both dimensions.

function out = boundedVarSize1(n) %#codegen
x = zeros(3,3);
coder.varsize("x",[5 5])
x = zeros(n,n);
out = x;
end

Generate MEX code for this function at the command line and inspect the code generation report. The code generator defines x as a :5x:5 array.

codegen boundedVarSize -args {0} -report

Code generation successful: View report

If you pass the generated MEX function a value greater than 5, you see a size overflow error. To avoid overflow errors, ensure that run-time inputs do not exceed the upper bounds defined by coder.varsize. Alternatively, rewrite your MATLAB code to prevent run-time size overflow.

function out = boundedVarSize2(n) %#codegen
x = zeros(3,3);
coder.varsize("x",[5 5])
if n <= 5
    x = zeros(n,n);
else
    x = zeros(5,5);
end
out = x;
end