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

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

Answer 1

[DGM]

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)

[Saumya Nagar 17BME0447]

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]

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')