MATLAB: Why does matlab give me a message that a never-used varible is undefined

undefinedvariable

The first part is the main M file, the second part is a function M file. When it is run, a message "Undefined function or method 'le' for input arguments of type 'sym' ". But the variable le is never used in the code. I don't know why. I will appreciate if anyone can help.
MeanShearstress=5 ;   %unit Pa
Density=1e3;
Ustar=sqrt(MeanShearstress/Density);
KinematicViscosity=1.004e-6;
D50=60e-6;
Roughness=2*D50;
RoughnessRenolds=Ustar*Roughness/KinematicViscosity;
CoefficientC=-0.993*log(RoughnessRenolds)+12.36;
Di=60e-6;
Protrusion=20e-6;
[MeanBedVelocity,Yb,Cd, Cl]=ProtrusionAssembly(Protrusion,Ustar,CoefficientC,D50,Di,KinematicViscosity);
function [MeanBedVelocity,Yb,Cd, Cl]=ProtrusionAssembly(Protrusion,Ustar,CoefficientC,D50,Di,KinematicViscosity)
Thickness=1.5*D50;
    Y1=0.25*Thickness;
    Y2=0.25*Thickness+Protrusion;
    syms y;
    Kapa=0.4;
    MeanBedVelocity=(int((Ustar*CoefficientC*y/Thickness)*sqrt((0.5*Di)^2-(y-Protrusion-Y1+0.5*Di)^2),y,Y1,Thickness)...
        +int((Ustar*(CoefficientC+log(y/Thickness)/Kapa))*sqrt((0.5*Di)^2-(y-Protrusion-Y1+0.5*Di)^2),y,Thickness,Y2))/(int(sqrt((0.5*Di)^2-(y-Protrusion-Y1+0.5*Di)^2),y,Y1,Y2));
    if MeanBedVelocity<=Ustar*CoefficientC
        Yb=(MeanBedVelocity*Thickness)/(Ustar*CoefficientC);
    else
        Yb=Thickness*exp(Kapa*(MeanBedVelocity/Ustar-CoefficientC));
    end;
      ParticleRenolds=MeanBedVelocity*Protrusion/KinematicViscosity;
      if ParticleRenolds<=1754
          Cd=(24/ParticleRenolds)*(1+0.15*ParticleRenolds^0.687);
      else
          Cd=0.36;
      end;
      if ParticleRenolds<8000
          Cl=Cd;
       end;

Best Answer

'le' is the printable name of the function <=
You are computing a result symbolically and attempting to compare the result using <= to some other value.
If you are sure that the symbolic result is a symbolic number with no remaining symbolic variables, then use double() to convert the symbolic result to a double precision number so it can be compared. This will, however, not work if there are any symbolic variables remaining in the expression.
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