Error using fzero with vectors

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Chris 2015-2-13

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编辑： per isakson 2015-2-13

Alright so I have this big huge complex formula and I am trying to solve it for AP2_AP1. My TA said I could use the fzero command and it would solve it for me. So I put it in a loop and I keep getting Operands to the and && operators must be convertible to logical scalar values.

Error in fzero (line 308)
    elseif ~isfinite(fx) || ~isreal(fx)

AP4_AP1 is a vector and I expect AP2_AP1 to be a vector too. Not sure how to fix this.

f= @(AP2_AP1)AP2_AP1.*(1-((Gamma-1).*(AP2_AP1-1))/sqrt((2.*Gamma).*(2*Gamma+(Gamma+1).*(AP2_AP1-1)))).^((-2.*Gamma)/(Gamma-1))-AP4_AP1; 
for i=1:1500
      fzero(f, 1)
      AW(i) = a*sqrt((Gamma+1)/(2*Gamma)*(AP1(i)/AP2(i)-1)+1); % Shock speed
end

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Answer 1

per isakson 2015-2-13

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https://ww2.mathworks.cn/matlabcentral/answers/178056-error-using-fzero-with-vectors#answer_167857

编辑：per isakson 2015-2-13

在 MATLAB Online 中打开

I think you should replace

(AP2_AP1-1))/sqrt

by

(AP2_AP1-1))./sqrt

to make f work with vectors.

&nbsp

Why do you expect AP2_AP1 is a vector? I think fzero requires that it is a scalar. However, I cannot find it stated in the documentation.

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Torsten 2015-2-13

在 MATLAB Online 中打开

fzero gives scalar input and expects scalar output.

I guess you want the following:

for i=1:length(AP4_AP1)
f=@(x) x*(1-((Gamma-1)*(x-1))/sqrt((2*Gamma)*(2*Gamma+(Gamma+1).*(x-1))))^((-2*Gamma)/(Gamma-1))-AP4_AP1(i);
z=fzero(f,1);
AP2_AP1(i)=z;
end

I assumed gamma is a scalar. If gamma is a vector, replace gamma by gamma(i).

Best wishes

Torsten.

per isakson 2015-2-13

编辑：per isakson 2015-2-13

I looked a bit harder. The documentation on fzero, Function to solve, says "Function to solve, specified as a handle to a scalar-valued function. fun accepts a scalar x and returns a scalar fun(x)."

You need a code that uses fzero with one element of AP4_AP1 at a time. Did you try Torstens code?

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Error using fzero with vectors

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