Strongly enforce SLSQP Bounds (#413)

* Strongly enforce SLSQP Bounds

* added test and clipping for final result

* update test

* fix typo

* isort and black fixes

* added warning

* use py opt warnings

* typo

* formatting fixes

---------

Co-authored-by: Marco Mangano <[email protected]>

pyoptsparse/pySLSQP/pySLSQP.py

@@ -12,6 +12,7 @@
 import numpy as np
 
 # Local modules
+from ..pyOpt_error import pyOptSparseWarning
 from ..pyOpt_optimizer import Optimizer
 from ..pyOpt_utils import try_import_compiled_module_from_path
 
@@ -166,7 +167,9 @@ def __call__(
             # SLSQP - Objective/Constraint Values Function
             # =================================================================
             def slfunc(m, me, la, n, f, g, x):
-                fobj, fcon, fail = self._masterFunc(x, ["fobj", "fcon"])
+                if (x < blx).any() or (x > bux).any():
+                    pyOptSparseWarning("Values in x were outside bounds during" " a minimize step, clipping to bounds")
+                fobj, fcon, fail = self._masterFunc(np.clip(x, blx, bux), ["fobj", "fcon"])
                 f = fobj
                 g[0:m] = -fcon
                 slsqp.pyflush(self.getOption("IOUT"))
@@ -176,7 +179,7 @@ def slfunc(m, me, la, n, f, g, x):
             # SLSQP - Objective/Constraint Gradients Function
             # =================================================================
             def slgrad(m, me, la, n, f, g, df, dg, x):
-                gobj, gcon, fail = self._masterFunc(x, ["gobj", "gcon"])
+                gobj, gcon, fail = self._masterFunc(np.clip(x, blx, bux), ["gobj", "gcon"])
                 df[0:n] = gobj.copy()
                 dg[0:m, 0:n] = -gcon.copy()
                 slsqp.pyflush(self.getOption("IOUT"))
@@ -220,6 +223,10 @@ def slgrad(m, me, la, n, f, g, df, dg, x):
             # fmt: on
             optTime = time.time() - t0
 
+            # Clip final result to user bounds (this occurs during the optimization as well
+            # so this just makes the output consistent with what the optimizer sees)
+            xs = np.clip(xs, blx, bux)
+
             # some entries of W include the lagrange multipliers
             # for each constraint, there are two entries (lower, upper).
             # if only one is active, look for the nonzero. If both are active, take the first one

pyoptsparse/pySLSQP/source/lsq.f

@@ -177,8 +177,20 @@ SUBROUTINE LSQ(M,MEQ,N,NL,LA,L,G,A,B,XL,XU,X,Y,W,JW,MODE)
           CALL DCOPY (N3, W(IW+M+N), 1, Y(M+N3+1), 1)
 
       ENDIF
+      call bound(n, x, xl, xu)
 
 C   END OF SUBROUTINE LSQ
 
       END
-
+
+      subroutine bound(n, x, xl, xu)
+      integer n, i
+      double precision x(n), xl(n), xu(n)
+      do i = 1, n
+         if(x(i) < xl(i))then
+            x(i) = xl(i)
+         else if(x(i) > xu(i))then
+            x(i) = xu(i)
+         end if
+      end do
+      end subroutine bound

tests/test_slsqp.py

@@ -0,0 +1,46 @@
+"""Test class for SLSQP specific tests"""
+
+# Standard Python modules
+import unittest
+
+# First party modules
+from pyoptsparse import OPT, Optimization
+
+
+class TestSLSQP(unittest.TestCase):
+    def test_slsqp_strong_bound_enforcement(self):
+        """
+        Test that SLSQP will never evaluate the function or gradient outside
+        the design variable bounds. Without strong bound enforcement, the
+        optimizer will step outside the bounds and a ValueError will be raised.
+        With strong bound enforement, this code will run without raising any
+        errors
+        """
+
+        def objfunc(xdict):
+            x = xdict["xvars"]
+            funcs = {}
+            if x[0] < 0:
+                raise ValueError("Function cannot be evaluated below 0.")
+            funcs["obj"] = (x[0] + 1.0) ** 2
+            fail = False
+            return funcs, fail
+
+        def sens(xdict, funcs):
+            x = xdict["xvars"]
+            if x[0] < 0:
+                raise ValueError("Function cannot be evaluated below 0.")
+            funcsSens = {
+                "obj": {"xvars": [2 * (x[0] + 1.0)]},
+            }
+            fail = False
+            return funcsSens, fail
+
+        optProb = Optimization("Problem with Error Region", objfunc)
+        optProb.addVarGroup("xvars", 1, lower=[0], value=[2])
+        optProb.addObj("obj")
+        opt = OPT("SLSQP")
+        sol = opt(optProb, sens=sens)
+        self.assertEqual(sol.optInform["value"], 0)
+        self.assertGreaterEqual(sol.xStar["xvars"][0], 0)
+        self.assertAlmostEqual(sol.xStar["xvars"][0], 0, places=9)