The code below explains program to evaluate a 2x2 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.

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Jai Khullar 2015-10-3

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https://ww2.mathworks.cn/matlabcentral/answers/246575-the-code-below-explains-program-to-evaluate-a-2x2-rotation-matrix-for-given-input-angle-the-code-see

编辑： Stephen23 2015-10-3

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.

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Answer 1

Stephen23 2015-10-3

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https://ww2.mathworks.cn/matlabcentral/answers/246575-the-code-below-explains-program-to-evaluate-a-2x2-rotation-matrix-for-given-input-angle-the-code-see#answer_194550

编辑：Stephen23 2015-10-3

在 MATLAB Online 中打开

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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Jai Khullar 2015-10-3

Seems I was taking the hard way. Is there really a need of assert command? please do answer this one! I'm new in matlab. Anyways it was helpful. Thanks!

Stephen23 2015-10-3

编辑：Stephen23 2015-10-3

The assert command fits into the category of "your function will work without it, but it is highly highly recommended". Using assert and checking input arguments is certainly a good habit to get into. The trick is to make the checking as minimal as possible, to allow your function to be a general as possible.

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The code below explains program to evaluate a 2x2 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.

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The code below explains program to evaluate a 2x2 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.

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