MATLAB: Use of cosine in a function

cosine problem

Hi everyone ! I had a little problem in cosine function.I use it in a small routine in order to calculate the circumscribed circle of a triangle parameters. I got this error message all the time : Attempted to access cos(0.523599); index must be a positive integer or logical.
The function is:
if true
  % function [Xp,Yp,R] = Cercle_circonscrit(Xa,Ya,Xb,Yb,Xc,Yc)
%distances calculating:
AB=sqrt((Xb-Xa)^2+(Yb-Ya)^2);
BC=sqrt((Xb-Xc)^2+(Yb-Yc)^2);
CA=sqrt((Xc-Xa)^2+(Yc-Ya)^2);
%scalar product:
scal_1=(Xb-Xa)*(Xc-Xa)+(Yb-Ya)*(Yc-Ya);
%angle Â:
cosA=scal_1/(AB*CA);
sinA=sqrt(1-cosA^2);
%radius of the circumscribed circle
R=BC/(2*sinA);
%coordinate of the center: 
cos=0.5*BC/R; sin=sqrt(1-cos*cos);
PP1=R*sin;
Xp1=0.5*(Xc+Xb);
Yp1=0.5*(Yc+Yb);
dx=Xc-Xb;
dy=Yc-Yb;
if dx==0
  c=0;
  if dy<=0
      s=-1;
  else
      s=1;
  end
else
c=cos(atan2(dx,dy)); s=sin(atan2(dx,dy)); 
end
Xps=Xp1-PP1*s;
Xpi=Xp1+PP1*s;
Yps=Yp1-PP1*c;
Ypi=Yp1+PP1*c;
APs=sqrt((Xps-Xa)^2+(Yps-Ya)^2);
if (APs-R)<=0.0001*R
  Xp=Xps;
  Yp=Yps;
else
  Xp=Xpi;
  Yp=Ypi;
end
end
It's like cosine is a table!
Thank's for your help !

Best Answer

Look at this line
cos=0.5*BC/R; sin=sqrt(1-cos*cos);
cos is used as a variable, then the function cos will not work. The same remark for sin
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