how to find cosine angle known the end points of 2 linesegments

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krishnasri 2015-4-28

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https://ww2.mathworks.cn/matlabcentral/answers/213891-how-to-find-cosine-angle-known-the-end-points-of-2-linesegments

评论： krishnasri 2015-5-5

采纳的回答： Guillaume

There are 2 line segments, known their end points, how can i find angle between them

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Guillaume 2015-4-29

This is basic math, that a simple web search would answer straight away

Note: you calculate the dot product of two vectors with dot and the norm with norm.

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Answer 1

Guillaume 2015-4-29

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The arguments you pass to dot and norm must be vectors not scalars

v1 = [1 1]
v2 = [0 3]
D = [v1;v2]; %possibly you have something like this
costheta = dot(D(1, :), D(2, :)) / (norm(D(1, :)) * norm(D(2, :)));
thetaindegrees = acosd(costheta)

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Answer 2

Roger Stafford 2015-4-29

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编辑：Roger Stafford 2015-4-29

在 MATLAB Online 中打开

Using 'atan2' or 'atan2d' and cross product is more accurate for angles that are near zero or near pi (180 degrees.)

a = atan2(norm(cross(D1,D2)),dot(D1,D2)); % Angle in radians

or

a = atan2d(norm(cross(D1,D2)),dot(D1,D2)); % Angle in degrees

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krishnasri 2015-5-5

I've around 60 such values in excel sheet and I need to calculate angle between all these points. How can I put the same in a loop for calculating it for 60 values?

D = xlsread('45_A.xls');

for i=1:60

CosTheta = dot(D(i,:),D(i+1,:))/(norm(D(i,:))*norm(D(i+1,:)));

ThetaInDegrees = acosd(CosTheta);

end

xslwrite('result',ThetaInDegrees);

but there is some error in the values. can u please help me

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