Any way to simultaneously solve 2 functions where the output of one is the input of another to avoid undefined variable error?

Hi All. I'm having a little trouble evaluating B in the function bidfn which involves finding the zeroes of the output of a nested function. More specifically, the output of bidfn is a function of stfna, but stfna takes the output of bidfn as an input argument. Trying to solve this leads to an error.

Just for some context, Dmr is the numerical solution to a first-order differential equation at the 101 points in A. srfna and stfna are my attempts to find sr and st in x=K(sr) and B=RR(st) respectively.

My problem is that B is the output of bidfn, which depends on stfna, which takes B as an input. This means that before I can solve for B in bidfn I have to specify B in stfna. How can I possibly solve for B and use B as input argument at the same time? Anytime I try to evaluate bidfn for a given x I get the following error:

Undefined function or variable "B".

     Error in bidfn/stfna (line 72)
     if B<=RR(1)

     Error in bidfn (line 15)
     st=stfna;

Now, I understand where this error comes from any why it occurs, that is not my problem. The part I need help with is writing the code in such a way as to avoid this problem altogether. What I'm asking is whether anyone may be able to rewrite/give me some advice about rewriting my code so that I can actually solve for B in bidfn? For example, is there are way to simultaneously solve bidfn and stfna to avoid the error?

Thanks in advance.

This is my code:

function B=bidfn(x)

%%%DEFINITIONS

K=Dmr;          % this is the solution to the ODE dmr/ds
A=0:0.01:1;     % this is the set of points K is solved at
for i=1:101     
 RR=A+K;        % this function combines the two
end 

%%%FUNCTION CALLS

fun=@ptesta;
sr=srfna;
st=stfna;

%%%B FUNCTION

if x<0.5
    B=0;

elseif x==0.5
    B=0.5;

elseif x>=0.5+K(101)
    B=x+0.5;

else
    x0=[0,1];
    B=fzero(fun,x0);
end

%%%NESTED FUNCTIONS

      %%%Nested function 1

      function C=ptesta

          for y=1:101
              z1=integral(A(y)+x,0,sr(y));
              z2=integral(RR(y),st(y),sr(y));
              C=(z1-z2)-B*st(y);
          end
      end 

      %%%Nested function 2

      function sr=srfna

          if x<=K(1)
              sr=0;

          elseif x>=K(101)
              sr=1;

          else
              for q=2:100
                  if x>=K(q-1) && x<K(q)
                      sr=A(q-1);
                  end
              end
          end
      end 

      %%%Nested function 3

      function st=stfna  

          if B<=RR(1)  
              st=0;

          elseif B>=RR(101)
              st=1;

          else
              for v=2:100
                  if B>=RR(v-1) && B<RR(v)
                      st=A(v-1);
                  end
              end
          end
      end

%%%END OF NESTED FUNCTIONS

end