finding magnitude of a vector (2024)

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Ashlianne Sharma on 7 Nov 2020

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Commented: Ashlianne Sharma on 8 Nov 2020

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Hi all, I am trying to make a function and the first step within my function is to find the magnitude of a vector that I have named on another script. How do I do this? I willo put my code below to explain more.

FROM FUNCTION PAGE

function[a, e, nu, i, O, m] = hw_COE_sharmaAshlianne(R, V)

% Inputs

% R = Radius vector [km]

% V = Velocity vector [km/s]

%

% Outputs

% a = semi major axis [km]

% e = eccentricity [no units]

% nu = true anomoly [degrees]

% i = inclination [degrees]

% O = right ascention of the ascending node(RAAN) [degrees]

% w = argument of perigee [degrees]

% Known values

m = 398600; % [km^3/s^2]

% Step one find the magnitude of the radius and velocity vectors

r = norm(R);

v = norm(V);

FROM SCRIPT

% Create a structure for our function to find COE parameters

Rvector = [15370 1400 21950]; % [km]

Vvector = [-0.1 3.84 -0.2]; % [km/s]

% Call function with the structured variables we created above

[a, e, nu, i, O, m] = hw_COE_sharmaAshlianne(Rvector, Vvector);

so to reiterate my question, how do I find the magnitude of Rvector that is defined in my script on my function page (STEP ONE IN FUNCTION)

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VBBV on 7 Nov 2020

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Edited: Walter Roberson on 8 Nov 2020

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>> hw_COE_sharmaAshlianne([...],[...])

Go to the command window and enter the vectors as shown above. Alternately run the script file in which the you are calling the function hw_COE_sharmaAshlianne(Rvector,Vvector)

Ashlianne Sharma on 7 Nov 2020

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I have done that, I made the separate script by which I call my function with

[a, e, nu, i, RAAN, w] = hw_COE_sharmaAshlianne(Rvector, Vvector);

just as I stated in my original question.

Again, the question I asked is how do I code to find the magnitude of the vector because as I put above, it does not work. I would appreciate if you help me with the question I asked??

r = norm(R);

v = norm(V);

I tried putting the lines

r = Rvector;

but that does not work.

VBBV on 8 Nov 2020

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Edited: Walter Roberson on 8 Nov 2020

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Since norm calculates the magnitude of the vector and is defined inside the function as

function[a,e,nu,i,O,m]=

w_COE_sharmaAshlianne(Rvector,Vvector)

...

r = norm(Rvector);

v = norm(Vvector)

...

end % close function file with end statement

Close function file with end

Ashlianne Sharma on 8 Nov 2020

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Okay that makes a lot of sense! I am still running into an issue here at these lines of code. The error message I am getting it that I don't have enough input arguments (regarding my Rvector and Vvector).

In order for me to define the Rvector and the Vvector on my script, how do I get those values onto my function page?

I don't know if I am making sense haha, I guess what I am trying to say is how do I call a function with specific values that will run through my function page if I dont explicitely define the R and V vectors on my function page?

VBBV on 8 Nov 2020

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Edited: VBBV on 8 Nov 2020

In function page just define the same variable vectors as defined in script file as shown in my message. Inside the function you don't require or have to define R and V again. Instead you pass the vectors Rvector and Vvector as arguments and use them with norm

VBBV on 8 Nov 2020

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If you delete the semicolon at the

norm(Rvector) norm(Vvector)

You can see the values of magnitude in command window once the run is completed .

Ashlianne Sharma on 8 Nov 2020

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Okay, so you had an amzing explaination for the norm aspect, thank you so much.

This question seems simple, But I struggle with this since the start of the class.

Script %note I changed Rvector to R for simplicity

% Define given vectors as variables

R = [15370 100 21950]; % [km]

V = [-0.1 3.84 -0.2]; % [km/s]

% Call function with the structured variables we created above

[a, e, nu, i, RAAN, w] = hw_COE_sharmaAshlianne(R, V);

Function: line one, after this line, I finished the rest of my code.

function[a, e, nu, i, RAAN, w] = hw_COE_sharmaAshlianne(R, V)

Question:

When I was getting your help, I just defined my vectors inside my function. Like you say above, you dont need to do this. I took out my defined vectors from my function and I now get an error message saying I do not have enough input arguments. I don't know how to pass the variables through. Like I know the variables have to be the same on the script and function page, But that isnt working for me. Any explaination on passing variables through the function would be great help... The matlab version online hasnt been too much of help. Thank you Vasishta!

VBBV on 8 Nov 2020

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Did you name the file exactly the same as function name? I.e. the name of the file which contains your function code and name of the function must be same. The name of file in which function code is present must be

hw_COE_sharmaAshlianne.

If you name something else then it will not run.

Ashlianne Sharma on 8 Nov 2020

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yeah I saved the file as the same name as my function. Everything was working until I removed the R and V vectors from the function file

Ashlianne Sharma on 8 Nov 2020

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So when I run my script that I call my function on, it works perfectly, however, I when I run my function file, i get the message that there are not enough input arguments

VBBV on 8 Nov 2020

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Oh. You seem to have changed the names of variables Rvector and Vvector in your script file from which you're calling function. Change it to

Rvector = [values] Vvector = [values]

VBBV on 8 Nov 2020

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Edited: VBBV on 8 Nov 2020

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Keep the same structure like before in the first post.

% if true

% code

% end

Rvector = [15370 1400 21950]; % [km]

Vvector = [-0.1 3.84 -0.2]; % [km/s]

%

[a, e, nu, i, O, m] = hw_COE_sharmaAshlianne(Rvector, Vvector);

VBBV on 8 Nov 2020

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Rvector, Vvector must have same names in script file and function file

Ashlianne Sharma on 8 Nov 2020

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okay, that makes sense. Just so I am understanding,

script

Rvector = [15370 1400 21950]; % [km]

Vvector = [-0.1 3.84 -0.2]; % [km/s]

%

[a, e, nu, i, O, m] = hw_COE_sharmaAshlianne(Rvector, Vvector);

Function

function[a, e, nu, i, RAAN, w] = hw_COE_sharmaAshlianne(Rvector, Vvector)

and everywhere in my code that R and V exist in my function, the variable should be Rvector and Vvector aswell?

VBBV on 8 Nov 2020

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Edited: VBBV on 8 Nov 2020

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https://in.mathworks.com/help/matlab/ref/function.html

Check the syntax of function declaration. You require space between the word function and output variable vector

%if true

% code

%end

function [a,e,nu,i,O,m]=

w_COE_sharmaAshlianne(Rvector,Vvector)

...

r = norm(Rvector);

v = norm(Vvector)

...

end % close function file with end statement

Ashlianne Sharma on 8 Nov 2020

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Okay, Thank you so much for your help!! i will definitely look more to the page you sent me, I think that may be very useful. Again, Thank you so much for taking So SO much time out to help me. I am just a struggling college student haha but yes, I really appreciate your time and help Vasishta!

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