structure inside a function

Hey all!

I am having a ton of issues with this line of code. So I have this equation in a function in which I have made the structure "inputs" with the different aircraft properties. in a separate script, I have called the function and labeled again the inputs from my function page. Along with this, I have named my vmax.

I keep getting the same error message of too many input arguments. What am I getting wrong?

D = (0.5*rho0*((vmax*1.687810)^2)*inputs.S*inputs.Cd0)+(((inputs.WS*inputs.S)^2)/(0.5*rho0*((vmax*1.687810)^2)*inputs.E*inputs.AR*inputs.S*pi));

[Ameer Hamza]

Can you show other parts of the code? Where are you creating the struct? How are you passing it to this function?

[KSSV]

Why did you hide the function names?

We cannot help you unless more details are given.

Also don't atatch your code as image snippet..copy and paste here.

[KSSV]

As you are suing inputs.S etc..ine formula...it is going to be an array....when you have array, you need to use element by element operations.

[Ashlianne Sharma]

This is the function page ( hid name for privacy but realize my name is on the account haha thank you for pointing that out)

function [V,D,P] = hw_dragPower_sharmaAshlianne(vmax, inputs)

% Function will return stall velocity, drag force, and power

% when given max velocity and aircraft properties are inputed,

% INPUTS:

% Maximum velocity(v_max) [m/s]

% aircraft properties [listed as a structure below]

% OUTPUTS:

% V: velocity vector from the stall velocity up to the maximum velocity [m/s]

% D: Drag vector [lbf]

% P: Power Vector [HP]

% KNOWNS:

T0 = 288.16; % [K] temp at sea level

rho0 = 0.0023765; % [slugs/ft^3] deinsity at sea level

R = 287; % [J/(kg k)] Gas constant of air

% list the properties in structures

% Baseline Aircraft Properties

inputs(1).WS = 6.9; %[lbf/ft^2] wing loading

inputs(1).AR = 6.5; % Aspect Ratio

inputs(1).Cd0 = 0.0373; % Parasite drag coefficient

inputs(1).E = 0.81; % Span efficiency

inputs(1).CLmax = 1.5; % Clean Maximum Lift

inputs(1).S = 179; % [ft^2] wing reference area

% Landing Configuration aircraft Properties

inputs(2).WS = 6.9; %[lbf/ft^2] wing loading

inputs(2).AR = 6.5; % Aspect Ratio

inputs(2).Cd0 = 0.042; % Parasite drag coefficient

inputs(2).E = 0.81; % Span efficiency

inputs(2).CLmax = 2.0; % Clean Maximum Lift

inputs(2).S = 179; % [ft^2] wing reference area

% Heavy wing loading aircraft

inputs(3).WS = 7.4; %[lbf/ft^2] wing loading

inputs(3).AR = 6.5; % Aspect Ratio

inputs(3).Cd0 = 0.0373; % Parasite drag coefficient

inputs(3).E = 0.81; % Span efficiency

inputs(3).CLmax = 1.5; % Clean Maximum Lift

inputs(3).S = 179; % [ft^2] wing reference area

% value for vmax

vmax = 85; % knots

% Naming output equations

D = (0.5*rho0*((vmax*1.687810)^2)*179*inputs.Cd0)+(((inputs.WS*179)^2)/(0.5*rho0*((vmax*1.687810)^2)*0.81*6.5*179*pi)); % [lbf]

P = D*(vmax*1.687810); % [HP] Power

V = ((inputs.WS*inputs.S)/(0.5*rho0*inputs.S*inputs.CLmax))^(0.5); % [m/s] Maximum stall velocity

end

script where I call my function

% HOUSEKEEPING

clc % Clear command window

clear % Clear variables in workspace

close all % Close any and all open figures

% Drag and Power (hw 2)

vmax = 85;

% list the properties in structures

% Baseline Aircraft Properties

inputs(1).WS = 6.9; %[lbf/ft^2] wing loading

inputs(1).AR = 6.5; % Aspect Ratio

inputs(1).Cd0 = 0.0373; % Parasite drag coefficient

inputs(1).E = 0.81; % Span efficiency

inputs(1).CLmax = 1.5; % Clean Maximum Lift

inputs(1).S = 179; % [ft^2] wing reference area

[V,D,P] = hw_dragPower_sharmaAshlianne(vmax, inputs);

outputs = [V,D,P];

[Ashlianne Sharma]

I just removed some of the structures from my formula to see if that would reduve the inputs (bc my error code said I had too many)

Can you explain what you mean by element by element?

[Stephen23]

"Can you explain what you mean by element by element?"

Most likely you should be using array operations (i.e. element-by-element), not matrix operations:

https://www.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

[Ashlianne Sharma]

I hear you, I looked over that page, thank you. However, I am specifically asked to use a structure. I am really concerned about my equation having too many input values.

[Stephen23]

"I am really concerned about my equation having too many input values."

As Ameer Hamza explained, the cause of the error is your inadvertent use of comma-separated lists generated from a non-scalar structure:

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

Why do you define inputs as an input to the function hw_dragPower_sharmaAshlianne but then overwrite this with data inside the function? What is the point of that?

[Ashlianne Sharma]

Just as I have commented below, this is the whole error message in my command window.

>> hw_dragPower_sharmaAshlianne(vmax, inputs)

Error using *

Too many input arguments.

Error in hw_dragPower_sharmaAshlianne (line 50)

D =

(0.5*rho0*((vmax*1.687810)^2)*179*inputs.Cd0)+(((inputs.WS.*inputs.S)^2)/(0.5*rho0*((vmax*1.687810)^2)*inputs.E.*inputs.AR.*inputs.S.*pi));

% [lbf]

Answer 1

[Ameer Hamza]

In your code 'inputs' is a 3-element array of struct. When you write

inputs.Cd0

It returns 3 values. If you want to multiply all three values with a number then you need to write it like this

a*[inputs.Cd0]; % 'a' is used as an example here.

In that case, you may also need to use element-wise operators: https://www.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

[Ashlianne Sharma]

oh, So I am meant to use brackets instead of nothing around the "inputs.Cd0"?

[Ashlianne Sharma]

This is now the message I am getting in my command window.

>> hw_dragPower_sharmaAshlianne(vmax, inputs)

Error using *

Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the

number of rows in the second matrix. To perform elementwise multiplication, use '.*'.

Error in hw_dragPower_sharmaAshlianne (line 50)

D =

(0.5*rho0*((vmax*1.687810)^2)*179*[inputs.Cd0])+((([inputs.WS]*[inputs.S])^2)/(0.5*rho0*((vmax*1.687810)^2)*[inputs.E]*[inputs.AR]*[inputs.S]*pi));

% [lbf]

[Ameer Hamza]

Yes, you need to use brackets. And I already mentioned that now you will need to use element-wise operators. For example

D = (0.5.*rho0.*((vmax*1.687810).^2).*[inputs.S].*[inputs.Cd0])+((([inputs.WS].*[inputs.S]).^2)./(0.5.*rho0.*((vmax.*1.687810).^2).*[inputs.E].*[inputs.AR].*[inputs.S].*pi));

I have replaed * with .* and / with ./. Read here: https://www.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

[Ameer Hamza]

Also make same changes in this line

V = (([inputs.WS].*[inputs.S])./(0.5.*rho0.*[inputs.S].*[inputs.CLmax])).^(0.5);

[Ashlianne Sharma]

For all of you that are helping me, you all are the smartest people ive ever talked to!

Ameer Hamza, sir, I think the way you explained this really helped! Now I understand that you must use brackets when using structure values in a function. You all taught me that the extra period goes between structures when multiplying or dividing the two (but not INSIDE the brackets) that is where I found one of my mistakes. Thanks to you all, I was able to fix my V equation aswell.

I just need to learn how to display the three output values as a vector. Thank you all so much for your help. I think you saved me from a mental breakdown.

[Ameer Hamza]

I am glad to be of help! :)

You can display the outputs as 3 sepeate vectors instead of combining in a single array

disp(V);
disp(D);
disp(P);

or you can combine them as column vectors in the matrix

outputs = [V.' D.' P .'];

Answer 2

[KSSV]

If you have two equal vectors, like:

a = rand(1,3) ;
b = rand(1,3) ; 
m = a.*b    % this should be used. This iscalled element by element multiplication
d = a./b    % element by element divison 
p = a*b    % this will trhow error. 
l = a/b     % this is not desired 

In your case: Try the below. If any error, try using .*, ./ at vectors multiplication and divison.

D = (0.5*rho0*((vmax*1.687810)^2)*inputs.S.*inputs.Cd0)+(((inputs.WS.*inputs.S).^2)./(0.5*rho0*((vmax*1.687810)^2)*inputs.E.*inputs.AR.*inputs.S*pi));

[Ashlianne Sharma]

I am still getting that there are too many input arguments..

I tried using the input.WS.

and I tried [input.WS.]

and [input.WS]

all of which gave me the same error code of too many input arguments

[KSSV]

Try like this. If not working check the size of each S, Cd0, WS etc.....If still there is a error. Share your code. There should be some other problem.

S = [input.S] ; 
Cd0 = [inputs.Cd0] ;
WS = [inputs.WS] ; 
E = inputs.E] ;
AR = [inputs.AR] ; 
D = (0.5*rho0*((vmax*1.687810)^2)*S.*Cd0)+(((WS.*S).^2)./(0.5*rho0*((vmax*1.687810)^2)*E.*AR.*S*pi));