Getting error that output argument is not assigned during function when it is?

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Shayma Al Ali 2021-11-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1595109-getting-error-that-output-argument-is-not-assigned-during-function-when-it-is

编辑： Stephen23 2021-11-25

I have a function that finds wind speeds between certain lats and lons. This is the first line in my function:

function [d,ccmp]=CCMPLidar2018(latmin,latmax,lonmin,lonmax)

This is my code for when I call the function:

[d,ccmp]=CCMPLidar2018(latmin,latmax,lonmin,lonmax);

It looks exactly alike right? However, I'm getting this error:

[d,ccmp]=CCMPLidar2018(latmin,latmax,lonmin,lonmax);

Output argument "ccmp" (and maybe others) not assigned during call to "CCMPLidar2018".

I just have no idea why I'm getting this error. The function and script are in the same folder, the argument ccmp is included in the function. Does anybody have any idea why I'm getting the error?

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Stephen23 2021-11-24

编辑：Stephen23 2021-11-24

"Does anybody have any idea why I'm getting the error?"

Yes: because the output is not defined inside the function. Just like the error message states.

"Getting error that output argument is not assigned during function when it is?"

Because it isn't.

This depends on the code in your function, not on the function signature (which you showed us).

Usually beginners get this error when they have some IF/ELSEIF/ELSE logic or SWITCH logic or something similar which does not define the output variables on all possible paths. But as you did not show any of the relevant code, we cannot debug this.

If you want more help, you will have to show us your function code.

Shayma Al Ali 2021-11-24

Here is the function code:

function [d,ccmp]=CCMPLidar2018(latmin,latmax,lonmin,lonmax)

%cd('G:\Shared drives\Saltzman Aydin lab data\Shayma\LIDAR\CCMP\2018')

d.lat=[]; d.lon=[]; d.wspd=[];d.time=[];d.dirname=[];d.fname=[]; d.uwind=[];

d.vwind=[];

direc=dir('*.nc');

for j=1:length(direc) %get data from each file

%disp(['working on...' scat_dir(j).name]);

fname={direc(j).name}; %file name as cell array

ccmp_lon=ncread(direc(j).name,'longitude');

ccmp_lat=ncread(direc(j).name,'latitude');

ccmp_time=ncread(direc(j).name,'time');

ccmp_uwind=ncread(direc(j).name,'uwnd');

ccmp_vwind=ncread(direc(j).name,'vwnd');

%get datenum and datetime

d.datenum=[];

for i=1:length(ccmp_time)

d.datenum(i,:)=addtodate(datenum(1987,1,1),fix(ccmp_time(i,:)),'hour');

end

d.datenum=d.datenum';

dt=datetime(d.datenum,'ConvertFrom','datenum');

%%get the data from two time dimensions and then average

%average two vectors from uwind and vwnd

uwnd1=squeeze(ccmp_uwind(:,:,1));

uwnd2=squeeze(ccmp_uwind(:,:,2));

uwnd3=squeeze(ccmp_uwind(:,:,3));

uwnd4=squeeze(ccmp_uwind(:,:,4));

vwnd1=squeeze(ccmp_vwind(:,:,1));

vwnd2=squeeze(ccmp_vwind(:,:,2));

vwnd3=squeeze(ccmp_vwind(:,:,3));

vwnd4=squeeze(ccmp_vwind(:,:,4));

wind1=sqrt(uwnd1.^2+vwnd1.^2); %calculate wind speed for first one

wind2=sqrt(uwnd2.^2+vwnd2.^2);

wind3=sqrt(uwnd3.^2+vwnd3.^2);

wind4=sqrt(uwnd4.^2+vwnd4.^2);

%calculate wind speedsfor every point

%wspd=(wind1+wind2+wind3+wind4)/4;

%find if scat lon and lat are valid and where

v_lat=ccmp_lat<=latmax & ccmp_lat >=latmin;

v_lat=find(v_lat==1); ccmp.lat=ccmp_lat(v_lat);

v_lon=ccmp_lon<=lonmax & ccmp_lon >=lonmin;

v_lon=find(v_lon==1);

ccmp.lon=ccmp_lon(v_lon);

%extract the wind speeds for specific region

%wspd dimensions is lonxlat so flip

wind1=wind1(v_lon,v_lat);

wind2=wind2(v_lon,v_lat);

wind3=wind3(v_lon,v_lat);

wind4=wind4(v_lon,v_lat);

%create 3 dimensional matrix of lat lon with time

%so (lat x lon x time) dimensions

ccmp.wind1(:,:,j)=wind1;

ccmp.wind2(:,:,j)=wind2;

ccmp.wind3(:,:,j)=wind3;

ccmp.wind4(:,:,j)=wind4;

%transpose the winds

% wind1=pagetranspose(wind1);

% wind2=pagetranspose(wind2);

% wind3=pagetranspose(wind3);

% wind4=pagetranspose(wind4);

%Get windspeeds for valid lat and lon

d.lat=ccmp.lat;

d.lon=ccmp.lon;

d.time=[d.time;dt];

save('ccpwind_2018.mat','d')

end

I guess its important to note that I've use this function various times before and just recently had this problem.

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Answer 1

Stephen23 2021-11-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1595109-getting-error-that-output-argument-is-not-assigned-during-function-when-it-is#answer_839589

编辑：Stephen23 2021-11-25

在 MATLAB Online 中打开

When direc is empty then ccmp is not defined (exactly as the error message states).

This error is easy to demonstrate (showing that the problem is in your code, not the function signature):

[A,B] = test([])
Output argument "y" (and possibly others) not assigned a value in the execution with "solution>test" function.
function [x,y] = test(z)
x = 1;
for k = 1:numel(z)
    y = 2;
end
end

The solution depends on what you want to do when no files are found: you could throw an error, search for some other files, or define a default value before the loop, e.g.:

ccmp = struct();

for j = ...

end

Note that the code overwrite some of ccmp's fields on each loop iteration.

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