How to solve my Error "Conversion to logical from sym is not possible" in my program" for Differential Relay equation

Hi Guys, I have a problem with this Error "Conversion to logical from sym is not possible" in my program" for Differential Relay equation.I want to find out about these coefficients "IS1 K1 IS2 K2" Thanks

   syms IS1 K1 IS2 K2 Idiff Ibias  ;
     Idiff=3    ;
   Ibias=1.5   ;
 if Ibias < IS2
    Idiff > (K1*Ibias+IS1)   %then trip

 elseif Ibias >= IS2 
   Idiff >= (K2*Ibias)-(K2-K1)*IS2 +IS1       %then trip
    end            

 %IS1:  The basic differential current setting
%K1:  The lower percentage bias setting
%IS2:  The bias current threshold setting
%K2:  The higher percentage bias setting

[madhan ravi]

To satisfy the logical operation it has to be a number for example IS2 value is not known.

[madhan ravi]

You cannot pass a logical statement to a symbolic variable.

[m gh]

for example IS1=1 ; ISD=2 now how to find a range for K1 and K2?