Error plotting fzero function - "Operands to the || and && operators must be convertible to logical scalar values"

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Saumya Nagar 17BME0447
评论： DGM 2021-4-9
Good Day!
I am trying to plot the solution of an equation using fzero function but getting the error - "Operands to the || and && operators must be convertible to logical scalar values". Can anyone please help me out.
The code is
clc;
clear all;
format short;
Throat_Diameter=2.8;
Exit_Diameter=5.76;
G=1.4;
Throat_Area=3.14159265.*(10.^(-6)).*((Throat_Diameter).^2)/4;
Exit_Area_inMeter=3.14159265.*(10.^(-6)).*((Exit_Diameter).^2)/4;
Diverging_Length= input('Enter the length of diverging section in mm: )' );
Distance_from_throat=linspace(1,Diverging_Length,50);
Section_Diameter=Throat_Diameter+((Exit_Diameter-Throat_Diameter)*Distance_from_throat)/Diverging_Length;
Section_Area=3.14159265.*(10.^(-6)).*((Section_Diameter).^2)/4;
ARatio=Section_Area/Throat_Area;
problem.objective = @(M) (1/M.^2).*(((2+(G-1).*M.^2)/(G+1)).^((G+1)/(G-1)))-ARatio.^2; % Objective function
problem.solver = 'fzero'; % Find the zero
problem.options = optimset(@fzero); % Default options
% Solve supersonic root
problem.x0 = [1+1e-6 50]; % Supersonic solver bounds
M_Local = fzero(problem); % Solve for supersonic M
plot(Distance_from_throat,M_Local)
The error is:
Operands to the || and && operators must be convertible to logical scalar values.
Error in fzero (line 421)
while fb ~= 0 && a ~= b
Error in PlottingAreaMachRelation (line 23)
M_Local = fzero(problem); % Solve for supersonic M

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采纳的回答

DGM
DGM 2021-4-7
编辑：DGM 2021-4-7
You've set Distance_from_throat to a vector. As far as I know, fzero() handles scalars only. You can always find all the solutions with a simple loop.
clc; clf
clear all;
format short;
Throat_Diameter=2.8;
Exit_Diameter=5.76;
G=1.4;
Throat_Area=3.14159265.*(10.^(-6)).*((Throat_Diameter).^2)/4;
Exit_Area_inMeter=3.14159265.*(10.^(-6)).*((Exit_Diameter).^2)/4;
Diverging_Length= 5;%input('Enter the length of diverging section in mm: )' );
DFT=linspace(1,Diverging_Length,50);
M_Local=zeros([1 numel(DFT)]);
for d=1:numel(DFT)
Distance_from_throat=DFT(d);
Section_Diameter=Throat_Diameter+((Exit_Diameter-Throat_Diameter)*Distance_from_throat)/Diverging_Length;
Section_Area=3.14159265.*(10.^(-6)).*((Section_Diameter).^2)/4;
ARatio=Section_Area/Throat_Area;
problem.objective = @(M) (1/M.^2).*(((2+(G-1).*M.^2)/(G+1)).^((G+1)/(G-1)))-ARatio.^2; % Objective function
problem.solver = 'fzero'; % Find the zero
problem.options = optimset(@fzero); % Default options
% Solve supersonic root
problem.x0 = [1+1e-6 50]; % Supersonic solver bounds
M_Local(d) = fzero(problem); % Solve for supersonic M
end
plot(DFT,M_Local)
  2 个评论
Saumya Nagar 17BME0447
Saumya Nagar 17BME0447 2021-4-9
Thanks a lot for the answer. It worked!
I have another question, here I now need to put three different numerical values of G and plot the result on a single plot. Is there an easy way to do it by putting a loop, if yes, can you please let me know how should I write it. Thanks in advance!
DGM
DGM 2021-4-9
The simple way would be to add another loop. If we arrange the y-series as rows in the output matrix, we can plot them all at once.
Throat_Diameter=2.8;
Exit_Diameter=5.76;
G=[1.2 1.4 1.6];
Throat_Area=3.14159265.*(10.^(-6)).*((Throat_Diameter).^2)/4;
Exit_Area_inMeter=3.14159265.*(10.^(-6)).*((Exit_Diameter).^2)/4;
Diverging_Length= 5;%input('Enter the length of diverging section in mm: )' );
DFT=linspace(1,Diverging_Length,10);
M_Local=zeros([numel(G) numel(DFT)]);
for g=1:numel(G)
for d=1:numel(DFT)
Distance_from_throat=DFT(d);
Section_Diameter=Throat_Diameter+((Exit_Diameter-Throat_Diameter)*Distance_from_throat)/Diverging_Length;
Section_Area=3.14159265.*(10.^(-6)).*((Section_Diameter).^2)/4;
ARatio=Section_Area/Throat_Area;
problem.objective = @(M) (1/M.^2).*(((2+(G(g)-1).*M.^2)/(G(g)+1)).^((G(g)+1)/(G(g)-1)))-ARatio.^2; % Objective function
problem.solver = 'fzero'; % Find the zero
problem.options = optimset(@fzero); % Default options
% Solve supersonic root
problem.x0 = [1+1e-6 50]; % Supersonic solver bounds
M_Local(g,d) = fzero(problem); % Solve for supersonic M
end
end
h=plot(DFT,M_Local); grid on
aa=num2cell(G);
tagfun=@(x) sprintf('G = %2.2f',x);
legend(h,cellfun(tagfun,aa,'UniformOutput',false),'location','northwest')

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