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if statement in a function

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Maja Zdulska
Maja Zdulska 2021-1-29
评论： Maja Zdulska 2021-1-30
Hi everyone,
I'm trying to create a function that will calculate wind direction from wind speed vectors u and v. I have the code presented below. However, it seems that the if loop is not taken into account (function outputs directions in the -180 to 180 degrees range). What am I doing wrong?
Thanks in advance.
function calc_wind_dir(filename)
%load data
data = readtable(filename);
%define wind variables, u is E-W component, v is N-S component
u = data{:,11};
v = data{:,12};
% The following code line gives wind angle relative to N, where:
% u is the W-E velocity (positive if the wind is blowing to the E from the W)
% v is the N-S velocity component (positive when blowing from S to N).
% j is sqrt(-1)
raw_direction=180*angle(v + j*u)/pi;
%The above measures where the wind is going rather than coming.
%In other words, the line of code above gives:
%E wind = Direction -90 dgrees
%W wind = Direction 90 dgrees
%S wind = Direction 0 degrees
%N wind = Direction 180 degrees
%The following will change the sign and indicate where the wind is coming from instead
direction=-180*angle(v + j*u)/pi;
%Here angles are measured positively (clockwise) and negatively (anti-clockwise) from N.
%(i.e. no angles will be bigger than +/-180 degrees).
%Below makes the wind more conventional (0-360 degrees).
if direction < 0
direction = direction + 360;
end
  2 个评论
dpb
dpb 2021-1-29
if is True iff all elements in the quantity are true; not what is wanted here.
Use logical indexing -- replace the if block with
direction(direction<0)=direction(direction<0) + 360;
You may want to save the logical vector for reuse as
isLZ=(direction<0);
direction(isLZ)=direction(isLZ)+360;
I'm not sure if the JIT optimizer is clever enough to recognize the common expression and avoid the recalculation or not.

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