For loop with constraint as a function

Hi,

Here is my code :

%Parameters%
  a=1.5;
  gamma=0.5
  lambda=0.07
  r=0.0025
  q=0.01
  z=0.3
  p=0.45
  dc=0.4  ;
  de=0.5 ;
  alphae=0.20 ;
  alphac=0.15;
  ratio1=(lambda*gamma*(1-p))/(r+q)
  ratio2=(lambda*gamma*p)/(r+q);
  upperlimity1=a;
  upperlimity2=a;
  y1bar1=z;
  y2bar1=z;
  y1bar2=z+de*(1+ratio1*(1-alphae));
  y2bar2=z+dc*(1+ratio2*(1-alphae)*(1-alphac));

     % Values%
     syms y1   y2  

D=(z+ratio1*(1-alphae)*y1)/(1+ratio1*(1-alphae));
E= (z+ratio2*(1-alphae)*(1-alphac)*y2)/(1+ratio2*(1-alphae)*(1-alphac));
F= (z+ratio2*(1-alphae)*(1-alphac)*y2bar2+ratio2*(1-alphae)*alphac*(y2bar2-dc))/(1+ratio2*(1-alphae)*(1-alphac)+ratio2*(1-alphae)*alphac);

    %%Function - Red line%%
    redline =solve(D==E, y2);
    pointB=solve(F== D, y1);

      %%Figure
    y2=0:0.01:a;
    plot(y1bar1,y2,'k-');
    hold on
    y2=0:0.01:a;
    plot(y1bar2,y2,'k-');
    hold on
    y1=0:0.01:a;
    plot(y1,y2bar1,'k-');
    hold on
    y1=0:0.01:a;
    plot(y1,y2bar2,'k-');
    hold on
    xlabel('Y1'); ylabel('Y2')

    y1=z:0.01:a ;
    y2=z:0.01:a;
   redline  = matlabFunction( redline );
    y1=y1bar1:0.01:pointB;   
    y2=y2bar1:0.01:y2bar2;
    plot(y1 , redline(y1),'r-');
    hold on

I have a black rectangle in the center of the figure. I want to compute an integral A for values of Y1 and Y2 on the right side of the red line Y2=f(Y1) and an integral B for values of Y1 and Y2 on the left side of the red line.

for y1=y1bar1: y1bar2;   
for y2=y2bar1: y2bar2;

I cannot write :

    for y2 > f(y1) % since y2=f(y1)

How can I manage to do that ? Thanks a lot, Mo