Why are all the negative values in the matrix show as 0?

The code below creates a matrix to do calculations, however, the negative values results are show in the matrix as 0. Why would this happen and how to keep those negative values instead of 0. Thank you.

load Foveal

T = ans; 
T_1002 = T(matches(T.message,'1002'),:);  
T_ENDSACC = T(matches(T.message,'ENDSACC'),:);
[x1 ~] = size(T_ENDSACC);
[x2 ~] = size(T_1002);  
T_diff = zeros(x1,x2);
for q = 1:x1
    T_diff(q,:) = T_ENDSACC.reltime(q) - T_1002.reltime(:);
end

Answer 1

[Voss]

reltime is of class uint32, as shown here:

load Foveal
T = ans;
class(T.reltime)

ans = 'uint32'

An unsigned integer cannot be negative. If you want to allow negative values use a different type such as a signed integer or a floating-point (such as single or double). Here I'll make reltime into a double:

T.reltime = double(T.reltime);

And then run the rest of the code:

T_1002 = T(matches(T.message,'1002'),:);
T_ENDSACC = T(matches(T.message,'ENDSACC'),:);
[x1 ~] = size(T_ENDSACC);
[x2 ~] = size(T_1002);  
T_diff = zeros(x1,x2);
for q = 1:x1
    T_diff(q,:) = T_ENDSACC.reltime(q) - T_1002.reltime(:);
end
T_diff

T_diff = 57×5

-870 -3140 -5422 -6504 -7398 -586 -2856 -5138 -6220 -7114 -361 -2631 -4913 -5995 -6889 -164 -2434 -4716 -5798 -6692 90 -2180 -4462 -5544 -6438 337 -1933 -4215 -5297 -6191 545 -1725 -4007 -5089 -5983 1171 -1099 -3381 -4463 -5357 1353 -917 -3199 -4281 -5175 1836 -434 -2716 -3798 -4692

Reference: https://www.mathworks.com/help/matlab/numeric-types.html

[JCH]

Thank you so so much!

[Voss]

You're welcome!

[Steven Lord]

FYI for the integer types you can use intmin and intmax to determine the range of allowed values for that type.

intmin('uint32')

ans = uint32 0

intmax('uint32')

ans = uint32 4294967295

Assignment of values outside that range truncates.

x = ones(1, 2, 'uint32')

x = 1×2

1 1

x(1) = -1 % -1 is < intmin('uint32') so MATLAB stores intmin('uint32')

x = 1×2

0 1

x(2) = 1e11 % 1e11 is > intmax('uint32') so MATLAB stores intmax('uint32')

x = 1×2

0 4294967295