Pretty simple on fzero

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Adam Stofko
Adam Stofko 2015-2-18
评论： Geoff Hayes 2015-2-19
I keep getting an error with the code bellow. I've gonna about this a couple of different way but still nothing. What I'm i going wrong?
function Trim
%Givens
delta=60000; %lbs
LCG=29; %ft
b=14; %ft
B=18; %degrees
V=67.5; %ft/s
a=1.39; %dt
f=0.5; %ft
e=4; % degrees
v=1.052e-5;
global x
%---------EQ's-------------
%C--------
Cv=3.18;
lamda= 64.267./ x^2.2;
C= LCG-(0.75-1./(5.21*(Cv./lamda)^2+2.39)*lamda*b);
%Df-------
V1= V*(1-0.0675./(lamda*cosd(x)))^(1/2);
Lk= lamda*b+(b*tand(B))./(2*pi*tand(x));
Re= V1*Lk./v;
Cf=0.075./(log10(Re)-2)^2;
Df= Cf*1.99*V1^2*lamda*b^2./(2*cosd(B));
%solve for Trim-------
X=fzero(@(x) delta.*((1-sind(lamda).*sind(x+e))./cosd(x).*C-f.*sind(x))+Df.*(a-f), 4)
end
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Adam Stofko
Adam Stofko 2015-2-18
Operands to the and && operators must be convertible to logical scalar values.
Error in fzero (line 308) elseif ~isfinite(fx) ~isreal(fx)
Error in Trim (line 37) X=fzero(@(x) delta.*((1-sind(lamda).*sind(x+e))./cosd(x).*C-f.*sind(x))+Df.*(a-f), 4)
Geoff Hayes
Geoff Hayes 2015-2-19
Adam - in the line
global x
what is x defined to be? If it hasn't been defined, then it is an empty matrix and so lambda is initialized to an empty matrix too. This seems to cause the error that you are observing. Please verify that x is initialized correctly and review whether it should be a global variable or just a local variable or an input to this function.

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回答（1 个）

Torsten
Torsten 2015-2-18
function call
X0=4;
X=fzero(@f,X0);
function y=f(x)
delta=60000; %lbs
LCG=29; %ft
b=14; %ft
B=18; %degrees
V=67.5; %ft/s
a=1.39; %dt
f=0.5; %ft
e=4; % degrees
v=1.052e-5;
%---------EQ's-------------
%C--------
Cv=3.18;
lamda= 64.267./ x^2.2;
C= LCG-(0.75-1./(5.21*(Cv./lamda)^2+2.39)*lamda*b);
%Df-------
V1= V*(1-0.0675./(lamda*cosd(x)))^(1/2);
Lk= lamda*b+(b*tand(B))./(2*pi*tand(x));
Re= V1*Lk./v;
Cf=0.075./(log10(Re)-2)^2;
Df= Cf*1.99*V1^2*lamda*b^2./(2*cosd(B));
y=delta.*((1-sind(lamda).*sind(x+e))./cosd(x).*C-f.*sind(x))+Df.*(a-f);
end
Best wishes
Torsten.

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