Loop and Conditional Statements

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Paulo Eduardo Beiral
评论： Paulo Eduardo Beiral 2021-6-24
I've got two vectors 1x366 u and v, and I have to make a new 1x366 vector of the arctg of u and v.
But I've got a few conditions depending if the respective value of u and v are negative or positive.
Here's some of the code which I started writing, but I am stuck.
Thank you for any help.
for n = 1:length(u)
if u(n) <0 && v(n) < 0
atan(v./u);
elseif u(n) > 0 && v(n) < 0
atan(u./v) + 4.712;
elseif u(n) < 0 && v(n) > 0
atan(u./v) + 1.571;
elseif u(n) > 0 && v(n) > 0
atan(v./u) + 3.142;
end
end
  2 个评论
Scott MacKenzie
Scott MacKenzie 2021-6-24
Have you looked at atan2? This is the four-quadrant version of atan -- might be what you need.
Paulo Eduardo Beiral
Paulo Eduardo Beiral 2021-6-24
Unfortunately atan2 wont help me in this case, I need exactly the atan with the conditions I entered in my code.
Thank you, mister.

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采纳的回答

Steven Lord
Steven Lord 2021-6-24
As written your code calls atan at most once per element of u but then throws that result away. You also have magic numbers that look like approximations to multiples of pi.
Instead I recommend using logical indexing.
base1 = atan(v./u);
base2 = atan(u./v);
result = NaN(size(u)); % determine what you want result to be if none of the cases hold
case1 = (u < 0) & (v < 0);
result(case1) = base1(case1);
case2 = (u > 0) & (v < 0);
result(case2) = base2(case2) + (3*pi/2);
% and similar for case3 and case4

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