function datan(y,x)
*
* Calculate four quadrants of phi from y and x
* Return answer in degrees
c DATAN runs from 0 to 360
c   It is 0 for (x,y)=(1,0), 90 for (x,y)=(0,1)
*
real x,y,phi,pi
pi=acos(-1.)

if(x.ne.0)then
 phi=180*atan(y/x)/pi
 if(y.ge.0)then
  if(x.ge.0)then
   datan=phi
  else
   datan=phi+180
  endif
 else
  if(x.ge.0)then
   datan=phi+360
  else
   datan=phi+180
  endif
 endif
else
 if(y.ge.0)then
  datan=90
 else
  datan=270
 endif
endif


*print *,x,y,datan
end