Error message the class x has no Constant property or Static method named y

I am trying to run the following code:

function [wind_directions,wind_speeds, de, relative_wind, ascending, wind_effectiveness] = we(absolute_yaw,wind_file,wind_row,pitch_angle)

%% James Kempton 11/06/2019

%% A function for calculating wind effectiveness

% load wind data

load(wind_file)

wind_directions=[wind.location_1(:,1),wind.location_2(:,1),...
    wind.location_3(:,1),wind.location_4(:,1),...
    wind.location_5(:,1),wind.location_6(:,1)];

wind_speeds=[wind.location_1(:,2),wind.location_2(:,2),...
    wind.location_3(:,2),wind.location_4(:,2),...
    wind.location_5(:,2),wind.location_6(:,2)];

% find difference in wind vector direction and heading vector direction

theta_diff=[absolute_yaw-wind.location_1(wind_row,1),...
    absolute_yaw-wind.location_2(wind_row,1),...
    absolute_yaw-wind.location_3(wind_row,1),...
    absolute_yaw-wind.location_4(wind_row,1),...
    absolute_yaw-wind.location_5(wind_row,1),...
    absolute_yaw-wind.location_6(wind_row,1)];

% calculate directional effectiveness

de=abs(cosd(theta_diff));

% assign headwind value 1

relative_wind=abs(theta_diff)>=90&abs(theta_diff)<=270;

relative_wind=double(relative_wind);

% assign tailwind value -1

relative_wind(relative_wind==0)=-1;

% assign ascent value 1

ascending=pitch_angle>0;

ascending=double(ascending);

% assign descent value -1

ascending(ascending==0)=-1;

% you know have 3 vectors, two a series of positive or negative ones and
% which together capture the phasing of the flight, and a third cpaturing
% the directional effectiveness. Together they are the wind effectiveness.

wind_effectiveness=ascending.*relative_wind.*de;

I receive this error message:

The class wind has no Constant property or Static method named 'location_1'.

Error in we (line 21)

theta_diff=[absolute_yaw-wind.location_1(wind_row,1),...

This is surprising given I can use wind.location_x up to line 21. Playing around I find that the function only allows wind.location_x if the index is (:,col). As soon as I try to specify specific rows the above error message arises.

I have attached the wind.mat table which is my wind_file above. Why does the above issue occur? How do I resolve it?

Thank you, James

Answer 1

[Walter Roberson]

load(wind_file)

In all current versions of MATLAB, when you load() inside a function without specifying an output for the load() call, and you load a variable whose name is the same as a function or class, then MATLAB is permitted to treat the name as referring to the function or class instead of to the variable.

You are loading a variable named wind but there is a class named wind and MATLAB will resolve to that class instead.

You should be using something like

loaded_vars = load(wind_file);
wind = loaded_vars.wind;

[James Kempton]

Thank you for this succinct and clear answer Walter, the problem is solved