MATLAB: The code below explains program to evaluate a 2×2 rotation matrix for given input angle.The code seems to be fine for all elements but one in1st row and second column.Can’t figure out where I’m wrong.

function [ var ] = rot( theta )
for j=1:2,
    for i=j:2,
        if (i==j)
            var(i,j) = cosd(theta);
        elseif (i-j>0)
            var(i,j) = sind(theta);
        else 
            var(i,j) = -sind(theta);
        end
    end
end
var;
end
The problem, is with var(1,2) which always displays a zero irrespective of angle value.

Best Answer

Using loops is very inefficient code. Try this instead:
function mat = rotmat2d(theta)
assert(isnumeric(theta)&&isscalar(theta),'Value must be a scalar numeric')
mat = [cosd(theta),sind(theta);-sind(theta),cosd(theta)];
end
and tested:
>> rotmat2d(0)
ans =
     1     0
     0     1
>> rotmat2d(90)
ans =
     0     1
    -1     0
>> rotmat2d(45)
ans =
      0.70711      0.70711
     -0.70711      0.70711
>> rotmat2d(180)
ans =
    -1     0
     0    -1
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