2D matrix indexing for element wise operation

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Raj Raj
Raj Raj 2016-2-19
编辑： Star Strider 2016-2-19
Hello all, I am using following code to estimate pairwise angle between for a vector. Where the angle should be between 0 to 2*pi. I am able to predict the angle. But I need your advise on implementing this two for loops. This is slowing the code. Looking forward for your attention. In the code, XYdata is a n x 2 matrix representing the Cartesian coordinates of individual point [xi, yi]. I presume this slow is because of two FOR loops.
for i2 =1:length(XYdata_new)
for j2 = 1:length(XYdata_new)
angle_ij(i2,j2)= Angle360(XYdata_new(i2,1), XYdata_new(i2,2), XYdata_new(j2,1),XYdata_new(j2,2));
end
end
Thanks in advance.
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Raj Raj
Raj Raj 2016-2-19
function angleout = Angle360(x1,y1,x2,y2)
if x1 == x2 && y1 ==y2
angleout = Inf;
end
angle = atan((y2-y1)/(x2-x1));
if angle > 0
if (y2 < y1) % y2 > y1, x2 > x1 % dy > 0, dx > 0 %first quadrant
angleout=pi+ angle;
else %
angleout= angle; % 3rd quadrant
end
elseif angle < 0
if x2 < x1 && y2 > y1
angleout= pi + angle; % 2nd quadrant
elseif y2 < y1 && x2 > x1
angleout= 3*pi/2 + (pi/2+angle); % 4th quadrant
elseif y2 < y1 && x2-x1 == 0
angleout= pi - angle; % 4th quadrant
end
elseif angle == 0
if x2 < x1
angleout = pi +angle;
else
angleout = angle;
end
end

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采纳的回答

Star Strider
Star Strider 2016-2-19
I would use the atan2 or atan2d functions. They are vectorised, so you can likely give your matrix columns to them directly and then do the angle difference calculations.
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Star Strider
Star Strider 2016-2-19
编辑：Star Strider 2016-2-19
My pleasure!
Thank you.
EDIT — More efficient versions of the angle conversion lines are:
Angles360 = rem(360+a, 360);
Angles2pi = rem(2*pi+a, 2*pi);

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