anchor.diff:  c     # in fclaw2d_map.c (C. Burstedde)
   c     # -------------------------------------------------------
   
  -      subroutine mapc2m_squareddisk(xc_in,yc_in,xp,yp,zp,user_double)
  +      subroutine mapc2m_squareddisk(xc,yc,xp,yp,zp,user_double)
         implicit none
   
         double precision xc_in,yc_in,xp,yp,zp
         double precision user_double(0:15)
         double precision half_length
  -      double precision R2sqrbyR1, R1byR2
  +      double precision R2sqrbyR1, R1byR2, R1, R2
         double precision xc1, yc1, xc, yc
         integer blockno, get_block
         logical l1,l2, u1, u2, iscorner
         logical c0, c1, c2, c3
  +      double precision pi
   
  +      common /compi/ pi
  +
  +      pi = 4.d0*atan(1.0)
   
         blockno = get_block()
   
  
positive.code:       else
           R2sqrbyR1 = user_double(0)
           R1byR2 = user_double(1)
  
           if (blockno .eq. 0) then
              xc1 = xc
              yc1 = 1.d0-yc
              call squareddisk_help(R2sqrbyR1, R1byR2,xc1,yc1,xp,yp)
              yp = -yp
           elseif (blockno .eq. 1) then
              xc1 = yc
              yc1 = 1.d0-xc
              call squareddisk_help(R2sqrbyR1, R1byR2,xc1,yc1,yp,xp)
              xp = -xp
           elseif (blockno .eq. 3) then
              xc1 = yc
              yc1 = xc
              call squareddisk_help(R2sqrbyR1, R1byR2,xc1,yc1,yp,xp)
           elseif (blockno .eq. 4) then
              xc1 = xc
              yc1 = yc
              call squareddisk_help(R2sqrbyR1, R1byR2,xc1,yc1,xp,yp)
           else
              write(6,*) 'mapc2m_squareddisk : Invalid block number'
              stop
  
negative.code: 
        end
  
        subroutine squareddisk_help(R1, R2,xi,eta,x,y)
        implicit none
  
        double precision xi, eta, x,y
        double precision R2sqrbyR1, R1byR2, R1, R2
        double precision R, tan_xi, xi_prime
  
        double precision pi, a
  
        common /compi/ pi
  
  c      R = R2sqrbyR1*R1byR2**(1.d0 + eta)
        R = (R2**(1-eta))*(R1**eta)
        tan_xi = tan(0.5d0*pi*(xi - 0.5d0))
        xi_prime = 2.d0*(1.d0 - eta)*(xi-0.5d0)+eta*tan_xi
  
  