# How to restrict input to set of sizes in an arguments block?

3 views (last 30 days)
Andreas Urbán on 18 Mar 2022
Answered: Steven Lord on 18 Mar 2022
I have a function with argument that should be either 2 x N or 3 x N size. Can't seem to figure out how to have that in an input block. Something similar to below (which isn't supported syntax):
arguments
myArg (2:3,:);
end

Steven Lord on 18 Mar 2022
I don't believe you can do this with the dimension validation alone. Nor would the existing validation functions help. So you're going to need to write your own, which I've done below as mustHaveTwoOrThreeRows. These first two cases work:
sample1674659(ones(2, 3))
ans = 6
sample1674659(ones(3, 3))
ans = 9
Specifying an input with the wrong number of rows will error, as will specifying an N-dimensional array (N > 2) (because of the dimension validation.)
try
sample1674659(ones(4, 3))
catch ME
fprintf("This case threw the error:\n\n%s\n", ME.message)
end
This case threw the error: Invalid argument at position 1. X must have either two or three rows.
try
sample1674659(ones(2, 3, 4))
catch ME
fprintf("This case threw the error:\n\n%s\n", ME.message)
end
This case threw the error: Invalid argument at position 1. Value must be a matrix.
function y = sample1674659(x)
arguments
x (:, :) {mustHaveTwoOrThreeRows(x)}
end
y = sum(x, 'all');
end
function mustHaveTwoOrThreeRows(x)
s = size(x, 1);
if ~(s == 2 || s == 3)
error('X must have either two or three rows.');
end
end

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