Merge branch 'better_wscreen' into tests

nifty_gridder.cc

@@ -594,8 +594,11 @@ template<typename T> class GridderConfig
     complex<T> wscreen(double x, double y, double w, bool adjoint) const
       {
       constexpr double pi = 3.141592653589793238462643383279502884197;
-      double n = cos(sqrt(x+y)), xn = 1./n;
-      double phase = 2*pi*w*(n-1);
+      double eps = sqrt(x+y);
+      double s = sin(eps);
+      double nm1 = -s*s/(1.+cos(eps));
+      double n = nm1+1., xn = 1./n;
+      double phase = 2*pi*w*nm1;
       if (adjoint) phase *= -1;
       return complex<T>(cos(phase)*xn, sin(phase)*xn);
       }

test.py

@@ -171,10 +171,11 @@ def test_pickling():
 
 
 @pmp('nx', [4, 18, 54])
-@pmp('dx', [1., 0.13, 132])
+@pmp('fov', [0.1, 1, 5])  # deg
 @pmp('w', [0, 10, 8489])
-def test_wstacking(nx, dx, w):
+def test_wstacking(nx, fov, w):
     np.random.seed(42)
+    dx = fov*np.pi/180/nx
     ny, dy = nx, dx
     conf = ng.GridderConfig(nx, ny, 1e-7, dx, dy)
     x, y = conf.Nu(), conf.Nv()