Test for scalar function inputs is failing - matlab

Question

Despite using isscalar, isinteger... the result after running is still true, I still had this test which is incorrect and in relation with Scalar values.
My program:
function valid = valid_date(year, month, day)
[y1 y2] = size(year);
[m1 m2] = size(month);
[d1 d2] = size(day);
if (mod(year,4)==0 && mod(year,100)~=0) || mod(year,400)==0
is_leap_year = 1;
else
is_leap_year = 0;
end
if ~(y1==y2==d1==d2==m1==m2==1)
valid = false;
elseif any(month == [1, 3, 5, 7, 8, 10, 12])
valid = (day >0 && day <= 31)
elseif any(month == [4, 6, 9, 11])
valid = day >0 && day <= 30;
elseif month == 2 && is_leap_year == 1
valid = (day >0 && day <=29);
elseif month == 2 && is_leap_year == 0
valid = (day >0 && day <=28);
else
valid = false;
end
end
The result after submitting my program, all tests are passed except the one related to scalar values:
Why did my program fail on the non-scalar test?

Answer 1

The way you're checking for scalars is really not well defined.
~(y1==y2==d1==d2==m1==m2==1)
This chained equivalence check is not the same as checking if all of your variables are equal to 1, consider the following counter-example:
1==0==0==1 % Output: 1
In this case none of your comparison variables should be 0, so you might skirt this issue, but it's still best to avoid it. You're also contending with floating point comparisons which are prone to issues.
You should use isscalar, you say you tried it but didn't show how. Something like this should work:
function valid = valid_date(year, month, day)
if ~( isscalar(year) && isscalar(month) && isscalar(day) )
valid = false;
return
end
% ... other code now we know inputs are scalar
end

Answer 2

Thank you so much #Wolfie. The problem is solved.
I used what you told me about and put it at the beginning of my function.
I show you guys the code, in case you had the same error:
function valid = valid_date(year, month, day)
if ~(isscalar(year) && isscalar(month) && isscalar(day))
valid = false;
return
end
if ((mod(year,4)==0 && mod(year,100)~=0) || mod(year,400)==0)
is_leap_year = 1;
else
is_leap_year = 0;
end
if any(month == [1, 3, 5, 7, 8, 10, 12])
valid = (day >0 && day <= 31);
elseif any(month == [4, 6, 9, 11])
valid = day >0 && day <= 30;
elseif (month == 2 && is_leap_year == 1)
valid = (day >0 && day <=29);
elseif (month == 2 && is_leap_year == 0)
valid = (day >0 && day <=28);
else
valid = false;
end
end
Yaaay all the tests are passed lhamdullah!