Make fit_flux=True the default when init=zero

Author: rmjarvis

piff/pixelgrid.py

@@ -57,7 +57,8 @@ class PixelGrid(Model):
     :param init:        Initialization method.  [default: None, which uses hsm unless a PSF
                         class specifies a different default.]
     :param fit_flux:    If True, the PSF model will include the flux value.  This is useful when
-                        this model is an element of a Sum composite PSF. [default: False]
+                        this model is an element of a Sum composite PSF. [default: False,
+                        unless init=='zero', in which case it is automatically True.]
     :param logger:      A logger object for logging debug info. [default: None]
     """
 
@@ -149,6 +150,12 @@ def initialize(self, star, logger=None, default_init=None):
                 # point for most uses of the zero initialization.
                 params *= 1.e-10
 
+                # Also, make sure fit_flux=True.  Otherwise, this won't work properly.
+                if not self._fit_flux:
+                    logger.info('Setting fit_flux=True, since init=zero')
+                    self._fit_flux = True
+                    self.kwargs['fit_flux'] = True
+
         elif init == 'delta':
             params = np.zeros(self.size**2)
             icenter = self._origin * self.size + self._origin