Question

I have written this function, and I have already defined values for rg and Lp, but still when I run this function it returns the error : (Input argument “Lr” is undefined.

Error in ==> Bis at 12
if f(Lr,rg,Xo)*f(Lr,rg,Xf)>0)

here is the function :

function[Lp,Xo,Xf]=Bis(Lr,rg)

Xo=0;
Xf=10;
Err=0.01;

syms x;
f=inline('(sqrt((2/3)*(((x*Lr)/3)-(x*x)+((2*x*x*x)/Lr)-((2*x*x*x*x)/(Lr*Lr))+(((2*x*x*x*x)/(Lr*Lr))*exp(-Lr/x))))-rg)');


    if f(Lr,rg,Xo)*f(Lr,rg,Xf)>0
        disp('The values you entered are not apropriate !')
        PlotLpFunction;
    Lp='unknown';
    elseif f(Lr,rg,Xo)*f(Lr,rg,Xf)==0
        if f(Lr,rg,Xo)==0
            Lp=Xo;
        elseif f(Lr,rg,Xf)==0
            Lp=Xf;
        end

    elseif f(Lr,rg,Xo)*f(Lr,rg,Xf)<0
        xi=(Xf-Xo)/2;
        while abs(f(Lr,rg,xi))>Err 
            if f(Lr,rg,xi)*f(Lr,rg,Xf)<0
                Xo=xi;
                xi=(Xo+Xf)/2;
            elseif f(Lr,rg,xi)*f(Lr,rg,Xf)>0
                Xf=xi;
                xi=(Xo+Xf)/2;   
            end
        end
        Lp=xi;
    end

Answer 1

The code executes for me on the newest version of Matlab, other than the fact that I don’t have the PlotLpFunction.

My initial impression was that you forgot to send the Lr (and all other argument) into you’re inlined f function, very easy to fix by adding them as arguments to the inline function. You’ll find the full usage in the official documentation.

The relevant part being

inline(expr,arg1,arg2,...) constructs an inline function whose input
arguments are specified by the strings arg1, arg2,…. Multicharacter
symbol names may be used.

but it seems to form the inline just fine by itself on both Matlab 2011b and 2008b, from context presumably. Answer is accepted now, so presumably that was the problem. Can anyone else reproduce his problem? If so please provide your Matlab version or other circumstances.