structure inside a function

2020 10 12
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更新时间：2020 10 12
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0 个投票

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));

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Ameer Hamza
Ameer Hamza 2020-10-12
Can you show other parts of the code? Where are you creating the struct? How are you passing it to this function?
KSSV
KSSV 2020-10-12
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
KSSV 2020-10-12
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
Ashlianne Sharma 2020-10-12
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
Ashlianne Sharma 2020-10-12
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
Stephen23 2020-10-12
"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
Ashlianne Sharma 2020-10-12
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
Stephen23 2020-10-12
编辑：Stephen23 2020-10-12
"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
Ashlianne Sharma 2020-10-12
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]

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 采纳的回答

Ameer Hamza
Ameer Hamza 2020-10-12
编辑：Ameer Hamza 2020-10-12

0 个投票

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

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Ashlianne Sharma
Ashlianne Sharma 2020-10-12
oh, So I am meant to use brackets instead of nothing around the "inputs.Cd0"?
Ashlianne Sharma
Ashlianne Sharma 2020-10-12
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
Ameer Hamza 2020-10-12
编辑：Ameer Hamza 2020-10-12
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
Ameer Hamza 2020-10-12
编辑：Ameer Hamza 2020-10-12
Also make same changes in this line
V = (([inputs.WS].*[inputs.S])./(0.5.*rho0.*[inputs.S].*[inputs.CLmax])).^(0.5);
Ashlianne Sharma
Ashlianne Sharma 2020-10-12
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
Ameer Hamza 2020-10-12
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 .'];

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更多回答（1 个）

KSSV
KSSV 2020-10-12
编辑：KSSV 2020-10-12

0 个投票

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));

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Ashlianne Sharma
Ashlianne Sharma 2020-10-12
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
KSSV 2020-10-12
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));

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