add warning about nu computation

bfps/DNS.py

@@ -694,6 +694,11 @@ class DNS(_code):
             opt.injection_rate = self.parameters['injection_rate']
         if type(opt.dealias_type) == type(None):
             opt.dealias_type = self.parameters['dealias_type']
+        if (opt.nx > opt.n or
+            opt.ny > opt.n or
+            opt.nz > opt.n):
+            opt.n = min(opt.nx, opt.ny, opt.nz)
+            print("Warning: '-n' parameter changed to minimum of nx, ny, nz. This affects the computation of nu.")
         self.parameters['nu'] = (opt.kMeta * 2 / opt.n)**(4./3)
         # check value of kMax
         kM = opt.n * 0.5