added broadcast: useful for subtracting mean flow

parallel.py

@@ -346,6 +346,49 @@ class PPP:
             # Iterate inplace from now on
             key = key_out
 
+    def broadcast(self,key,arg,operation):
+        '''Broadcasts an inplace operation involving a scalar or matrix on 
+        the entire grid. If 'arg' is a matrix, it must be three-dimensional
+        and its axes must be singular or of length nx/ny/nz.'''
+        import numpy as np
+        import operator
+        if operation in ('add','+'):
+            op = operator.iadd
+        elif operation in ('subtract','sub','-'):
+            op = operator.isub
+        elif operation in ('divide','div','/'):
+            op = operator.itruediv
+        elif operation in ('multiply','mul','*'):
+            op = operator.imul
+        elif operation in ('power','pow','^','**'):
+            op = operator.ipow
+        else:
+            raise ValueError("Invalid operation: {}".format(operation))
+        if isinstance(arg,np.ndarray):
+            sl_arg = 3*[slice(None)]
+            for axis in range(3):
+                if arg.shape[axis]==1:
+                    continue
+                elif arg.shape[axis]==self.proc_grid[key][2*axis+1][-1]:
+                    pos = self.position_from_rank(self.rank,external=False)[axis]
+                    sl_arg[axis] = slice(
+                        self.proc_grid[key][2*axis][pos]-1,
+                        self.proc_grid[key][2*axis+1][pos])                
+                else:
+                    raise ValueError("'arg' must either be singular or match global "\
+                                     "grid dimension. (axis={}: got {:d}, expected {:d}".format(
+                                     axis,arg.shape[axis],self.proc_grid[key][2*axis+1][-1]))
+            # Only operate on interior and communcate ghosts later
+            sl_int = tuple(slice(self.num_ghost[ii],-self.num_ghost[ii]) for ii in range(3))
+            sl_arg = tuple(sl_arg)
+            op(self.field[key].data[sl_int],arg[sl_arg])
+            # Exchange ghost cells and set boundary conditions
+            self.exchange_ghost_cells(key)
+            self.impose_boundary_conditions(key)
+        elif isinstance(arg,(int,float)):
+            op(self.field[key].data,arg)
+        return
+
     def vtk_contour(self,key,val):
         '''Compute isocontour for chunks.'''
         if any([self.num_ghost[ii]>1 for ii in range(3)]):