fix: if interpolator results in 0, still set up to date

otherwise interpolator won't stop solving!

Author: lachlangrose

LoopStructural/interpolators/_discrete_interpolator.py

@@ -1,6 +1,7 @@
 """
 Discrete interpolator base for least squares
 """
+
 import logging
 
 from time import time
@@ -304,9 +305,6 @@ def add_equality_constraints(self, node_idx, values, name="undefined"):
         }
         self.eq_const_c += idc[outside].shape[0]
 
-    def add_non_linear_constraints(self, nonlinear_constraint):
-        self.non_linear_constraints.append(nonlinear_constraint)
-
     def add_inequality_constraints_to_matrix(self, A, l, u, idc, name="undefined"):
         """Adds constraints for a matrix where the linear function
         l < Ax > u constrains the objective function
@@ -785,7 +783,7 @@ def solve_system(self, solver="cg", **kwargs):
         if np.all(self.c[self.region] == 0):
             self.valid = False
             logger.warning("No solution, scalar field 0. Add more data.")
-
+            self.up_to_date = True
             return
         self.valid = True
         logging.info(f"Solving interpolation took: {time()-starttime}")