Help with Colebrook equation and f zero command.

I am trying to do a problem with the colebrook equation in which I have to find the roots of the equation to find "f". I am trying to use the fzero command along with a function file, but it is not working. How do I do this?

function f = fricfactor(f) Re = linspace(10e4,10e7,31); f = (1/sqrt(f))-2*log10(Re*sqrt(f))-0.8; end

 fcw = fzero(@fricfactor,[0 1]);

Answer 1

[Torsten]

f=@(x)(1/sqrt(x)-2*log10(Re*sqrt(x))-0.8);

Re=10000;

Delta_Re=200;

for i=1:20

fcw(i)=fzero(f,[1e-8 1]);

Reynolds(i)=Re;

Re=Re+Delta_Re;

end

Best wishes

Torsten.

[Yianni]

Thank you!

[Yianni]

Im actually getting this error when I do this:

Error: File: prac.m Line: 10 Column: 15 "f" was previously used as a variable, conflicting with its use here as the name of a function or command. See "How MATLAB Recognizes Command Syntax" in the MATLAB documentation for details.

[Yianni]

I get this specifically for your work:

Operands to the and && operators must be convertible to logical scalar values.

Error in fzero (line 423) while fb ~= 0 && a ~= b

Error in prac2 (line 9) fcw(i)=fzero(f,[1e-8 1]);

Answer 2

[Torsten]

Re=10000;

f=@(x)(1/sqrt(x)-2*log10(Re*sqrt(x))-0.8);

fcw = fzero(f,[1e-8 1]);

If you want to determine fcw for different Reynolds numbers, you will have to do that in a for Loop.

Best wishes

Torsten.

[Yianni]

Yes I want to use a looping structure, but where could I do this in this function file?