Set cell size in test_holo_from_correlations based on maximum frequency

test.py

@@ -348,20 +348,23 @@ def test_against_wdft(nxdirty, nydirty, nchan, nrow, fov):
 @pmp('nxdirty', (32,16))
 @pmp('nydirty', (32,64))
 @pmp("nrow", (100,1000))
-@pmp("nchan", (1,))
+@pmp("nchan", (1,5))
 @pmp('epsilon', (1e-3,1e-6))
 def test_holo_from_correlations(nxdirty, nydirty, nchan, nrow, epsilon):
     np.random.seed(420)
     uvw = np.random.randn(nrow, 3)
     uvw[:, 2] = 0
-    cell = 0.75/(2*np.abs(uvw).max())
+    lightspeed, f0 = 3e8, 1e9
+    freq = f0 + np.arange(nchan)*(f0/nchan)
+    fmax = freq.max()
+    # Nyquist sampling
+    uv_max = np.abs(uvw * fmax/lightspeed).max()
+    cell = 0.75/(2*uv_max)
     conf = ng.GridderConfig(nxdirty=nxdirty,
                             nydirty=nydirty,
                             epsilon=epsilon,
                             pixsize_x=cell,
                             pixsize_y=cell)
-    f0 = 3e8
-    freq = f0 + np.arange(nchan)*(f0/nchan)
     bl = ng.Baselines(coord=uvw, freq=freq)
     flags = np.zeros((nrow, nchan), dtype=np.bool)
     idx = ng.getIndices(bl, conf, flags)