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I have made function in Matlab, that shale calculate the rotation matrix for fi degrees around unit vector k.

function R = rot(k,fi)     rad = fi*(pi/180);      % This is just to make it easyer to read!     x = k(1);     y = k(2);     z = k(3);      % Create a 3x3 zero matrix     R = zeros(3,3);     % We use the formual for rotationg matrix about a unit vector k      R(1,1) = cos(rad)+x^2*(1-cos(rad));     R(1,2) = x*y*(1-cos(rad))-z*sin(rad);     R(1,3) = x*z*(1-cos(rad))+y*sin(rad);      R(2,1) = y*x*(1-cos(rad))+z*sin(rad);     R(2,2) = cos(rad)+y^2*(1-cos(rad));     R(2,3) = y*z*(1-cos(rad))-x*sin(rad);      R(3,1) = z*x*(1-cos(rad))-y*sin(rad);     R(3,2) = z*y*(1-cos(rad))+x*sin(rad);     R(3,3) = cos(rad)+z^2*(1-cos(rad)); end 

But it don't seem to work, i have a test rules

rot(k,0) == I rot(k,fi) == rot(k,fi+360) rot(-k,fi) == transpose(rot(k,fi)) rot(k,f1)*rot(k,f2) == rot(k,f1+f2) rot(k,fi)*k == k 

My function is always successfull on rule nr 1, 3 and sometime on 2. What am i doing wrong here? is my function not correct?

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    The diffrence are small! example sometime are 0 compared with a -02012-10-24

1 Answers 1

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You are using equality checks on floating point values.

I suggest you do not check for equality but see whether the absolute difference is less than epsilon.