Changing the atan function so that it ranges from 0 to 2*pi

Question

KA 2011-6-12

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评论： theodore panagos 2023-8-6

I know that the matlab atan function returns values in the range of -pi/2 to pi/2. How do i change it so that it goes over the full range 0 to 2*pi?

My first attempt was using a while loop, but it was incorrect.

I need to write a function mfile to set the built-in matlab function atan in the range of 0 to 2*pi without using atan2. im new to matlab so im unsure of what to do.

Thank you

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wenjun kou 2017-3-8

编辑：wenjun kou 2017-3-8

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Although you don't want to use atan2, I thought I might just put this out there since atan2 returns a range between -pi to pi:

a = atan2(y, x); 
a = a .* (a >= 0) + (a + 2 * pi) .* (a < 0);

Stephen23 2018-10-27

See Daniel Svedbrand's answer for the simplest solution.

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Answer 1

Daniel Svedbrand 2018-9-14

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编辑：John D'Errico 2023-8-3

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Adding mod 2*pi to atan2 should work just fine

z = mod(atan2(y,x),2*pi);

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Feruza Amirkulova 2023-8-3

Yes, mod(atan2(y,x),2*pi) worked and its gradients are the same as for (atan2(y,x)).

John D'Errico 2023-8-3

Edited to remove profanity in the answer.

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Answer 2

Walter Roberson 2011-6-12

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Use atan2() instead.

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Paulo Silva 2011-6-12

I didn't include that statement on purpose, when none of the others if statements are true the value of v is NaN, you could also do this:

if isnan(v)

error('Arguments must be different from zero')

end

KA 2011-6-12

ok, did not know that, thanks again

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Answer 3

Paulo Silva 2011-6-12

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The Wikipedia got all explained, you just need to do the code, it's very simple.

function v=myatan(y,x)
if nargin==1 %just in case the user only gives the value of y myatan(y)
    x=1;
end
v=nan;
if x>0
    v=atan(y/x);
end
if y>=0 & x<0
    v=pi+atan(y/x);
end
if y<0 & x<0
    v=-pi+atan(y/x);
end
if y>0 & x==0
    v=pi/2;
end
if y<0 & x==0
    v=-pi/2;
end
if v<0
    v=v+2*pi;
end
end

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KA 2011-6-12

thanks, very helpful

Mehmet Can Türk 2022-4-9

编辑：Mehmet Can Türk 2022-4-9

I checked the Wikipedia link and tested the code. First of all, thank you so much for the contribution.

I wanted to convert atan2 function from Matlab into another environment which supports only atan function. So I deleted the if block and everything worked perfectly.

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Answer 4

Kent Leung 2018-3-21

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编辑：Kent Leung 2018-3-21

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Better late than never. (Also posting as a future reference to myself.) The function below accepts y & x as vectors in Matlab. Rather than using 'if' statements, the below might be faster if there is some parallelization implemented in the built-in index searching.

Note: I have a slight disagreement with the above for the x>0 & y<0 case, as well as the for x=0 & y<0 case. The code below gives 0 to 2pi.

   function v=myatan(y,x)
   %---returns an angle in radians between 0 and 2*pi for atan
   v=zeros(size(x));
   v(x>0 & y>=0) = atan( y(x>0 & y>=0) ./ x(x>0 & y>=0) );
   v(x>0 & y<0) = 2*pi+atan( y(x>0 & y<0) ./ x(x>0 & y<0) );
   v(x<0 & y>=0) = pi+atan( y(x<0 & y>=0) ./ x(x<0 & y>=0) );
   v(x<0 & y<0) = pi+atan( y(x<0 & y<0) ./ x(x<0 & y<0) );
   v(x==0 & y>=0) = pi/2;
   v(x==0 & y<0) = 3/2*pi;
   end