Select norm in parameter

README.md

@@ -108,6 +108,11 @@ should be a `;` sperated list of `key=value` pairs. The possible keys are
 * `max_delta` (double, default 1e-2): when using the adaptive step, do not
   exceet `delta_max`.
 
+* `adaptive_norm`: norm to use to estimate the error of the adaptive method:
+  `L1` (default) for the normalized L1 norm, `k3` for the normalized L1 norm of
+  f_k/|k|^3, `k32` for the normalized L1 norm, `enstrophy` for the enstrophy
+  norm.
+
 
 # Interrupting/resuming the computation