Use .mat file as input argument in a function.

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Tunde Adubi 2022-4-3

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https://ww2.mathworks.cn/matlabcentral/answers/1687499-use-mat-file-as-input-argument-in-a-function

评论： Tunde Adubi 2022-4-7

SD.jpg

Assuming a Data.mat file has a table of rows and columns, how can it be used as input arguement so that the elements in any row/column be called up for use in the function?

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Answer 1

Siddharth Bhutiya 2022-4-5

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https://ww2.mathworks.cn/matlabcentral/answers/1687499-use-mat-file-as-input-argument-in-a-function#answer_935680

在 MATLAB Online 中打开

If you look at the value of K in your screenshot you will notice that it is a struct and one of the fields would be the table you are looking for (the name would be the name that you used while creating the MAT file). Once you figure out the name you can use the dot syntax to pass that as input to another function.

>> K = load("data.mat")
K = 
  struct with fields:
    myTable: [4×4 table]
>> SVdata(K.myTable)

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Stephen23 2022-4-6

编辑：Stephen23 2022-4-7

在 MATLAB Online 中打开

"but the the .mat file can't be used as input argument in a function using the dot syntax,..."

It is very common to provide structures and/or their fields as inputs to functions.

"...and that is where the problem lies."

What is much more likely is that you are doing something wrong. Lets have a look at your code (which you unfortunately uploaded as screenshots. In future please upload code as text).

K.T is not valid in a function signature like that, just like it is not possible to use any other indexing inside the function signature line. Do not do that.

On the 3rd and 4th lines of the function you wrote K.T, so clearly K should be the input argument, like this:

function [Xt,Yt,Zt] = SVdata(K)
%                            ^ indexing is not allowed here!

We can also see that although your script loads the data into structure K, you then do nothing with K and also do not call the local function. So your code ignores the imported data and does absolutely nothing with that function. Notice how MATLAB has underlined the function name (because it is unused): do not ignore these warnings.

Solution: you need to actually call the function with its required input arguments:

S = load(..);
[outX,outY,outZ] = SVdata(S)

There may be other bugs in your code, but because you did not upload text I could not check it.

Tunde Adubi 2022-4-7

在 MATLAB Online 中打开

S=load('SatData.mat');
SVdata(S.T)
function [Xt, Yt, Zt] = SVdata(K)
%  Constants
u = 3.986005e14;					% earth gravitational constant (m^3/s^2)
Omega_e = 7.2921151467e-5;	     	% earth's rotation rate (rad/sec)
% Almanac Parameters 
e = K(1,2);      % eccentricity: 
a = K(1,7)^2;         %semi-major Axis                      
t_oe = K(1,4); % epoch orbital time of applicability
i=   K(1,5);           %Orbital Inclination(rad):
w = K(1,9)	;            %Argument of Perigee(rad):   
Mo =   K(1,10);    %Mean Anomaly at (rad):  
Omega_n= K(1,8); %Right Ascen at Week(rad): 
Omega_dot = K(1,8);     %Rate of Right Ascen(r/s): 
t=t_oe + (1/2)*3600;        % GPS time
t_k=t-t_oe;					% Time from eph ref epoch (s)
n=sqrt(u/a^3);                   %mean motion
M=Mo+n*t_k;						% Mean anomaly (rad/s)
% Eccentricity Anomaly Iteration
E=0;
for z =1:100
    E = M +e*sin(E);
end
E = M+e*sin(E); % Eccentric Anomaly
r = a*(1-(e*cos(E))); %orbit radius
v = atan2(sqrt(1-e^2)*sin(E), cos(E)-e); % true Anomaly
% SV coordinates in rotated orbit
xp=r*cos(w+v);
yp=r*sin(w+v); 
Omega_p= Omega_n + (Omega_dot - Omega_e)*(t_k)-(Omega_e)*t_oe;
%This converts SV position to ECEF coordinates
Xt =xp*cos(Omega_p) - yp*sin(Omega_p)*cos(i);
Yt=xp*sin(Omega_p) - yp*cos(Omega_p)*sin(i);
Zt =yp*sin(i);
fprintf('%9s %22.11f\n','Omega_p',Omega_p);
fprintf("The Satellite ECEF coordinates for PRN1 are:\n")
fprintf('\n%9s %22.11f\n','Xt',Xt);
fprintf('%9s %22.11f\n','Yt',Yt);
fprintf('%9s %22.11f\n','Zt',Zt);
end

Yeah,Thanks. It looks good. However, i am having unrecognized function error whenever i tied to call the function from command window.

Stephen23 2022-4-7

编辑：Stephen23 2022-4-7

"However, i am having unrecognized function error whenever i tied to call the function from command window. "

Because you have written a script, not a function file.

As I already explained in this comment, you cannot write a script and also call the local function from the command line. That simply will not work. Just as I wrote before, you need to decide:

if you want to be able to call the function from the command line then you need to get rid of all code that is not within function...end . See: https://www.mathworks.com/help/matlab/ref/function.html
if you really want a script (as you have now), then you cannot call the local function from the command line. See: https://www.mathworks.com/help/matlab/matlab_prog/local-functions-in-scripts.html

You have to decide what you want to do.

Tunde Adubi 2022-4-7