Warn user if using power law without constraint

pysr/sr.py

@@ -104,6 +104,16 @@ def _process_constraints(binary_operators, unary_operators, constraints):
             constraints[op] = -1
     for op in binary_operators:
         if op not in constraints:
+            if op in ["^", "pow"]:
+                # Warn user that they should set up constraints
+                warnings.warn(
+                    "You are using the `^` operator, but have not set up `constraints` for it. "
+                    "This may lead to overly complex expressions. "
+                    "One typical constraint is to use `constraints={..., '^': (-1, 1)}`, which "
+                    "will allow arbitrary-complexity base (-1) but only powers such as "
+                    "a constant or variable (1). "
+                    "For more tips, please see https://astroautomata.com/PySR/tuning/"
+                )
             constraints[op] = (-1, -1)
         if op in ["plus", "sub", "+", "-"]:
             if constraints[op][0] != constraints[op][1]: