Add getBase and setBase methods to LP class

Author: Joao-Dionisio

src/pyscipopt/lp.pxi

@@ -531,6 +531,70 @@ cdef class LP:
 
         return binds
 
+    def getBase(self):
+        """Returns the basis status of columns and rows.
+
+        Column status values: SCIP_BASESTAT_LOWER (0), SCIP_BASESTAT_BASIC (1),
+        SCIP_BASESTAT_UPPER (2), SCIP_BASESTAT_ZERO (3).
+
+        Row status values: SCIP_BASESTAT_LOWER (0), SCIP_BASESTAT_BASIC (1),
+        SCIP_BASESTAT_UPPER (2).
+
+        Returns
+        -------
+        tuple of (list of int, list of int)
+            Column basis statuses and row basis statuses.
+
+        """
+        cdef int ncols = self.ncols()
+        cdef int nrows = self.nrows()
+        cdef int* c_cstat = <int*> malloc(ncols * sizeof(int))
+        cdef int* c_rstat = <int*> malloc(nrows * sizeof(int))
+        cdef int i
+
+        PY_SCIP_CALL(SCIPlpiGetBase(self.lpi, c_cstat, c_rstat))
+
+        cstat = [c_cstat[i] for i in range(ncols)]
+        rstat = [c_rstat[i] for i in range(nrows)]
+
+        free(c_rstat)
+        free(c_cstat)
+
+        return cstat, rstat
+
+    def setBase(self, cstat, rstat):
+        """Sets the basis status of columns and rows.
+
+        Column status values: SCIP_BASESTAT_LOWER (0), SCIP_BASESTAT_BASIC (1),
+        SCIP_BASESTAT_UPPER (2), SCIP_BASESTAT_ZERO (3).
+
+        Row status values: SCIP_BASESTAT_LOWER (0), SCIP_BASESTAT_BASIC (1),
+        SCIP_BASESTAT_UPPER (2).
+
+        Parameters
+        ----------
+        cstat : list of int
+            Column basis statuses (length must equal ncols).
+        rstat : list of int
+            Row basis statuses (length must equal nrows).
+
+        """
+        cdef int ncols = len(cstat)
+        cdef int nrows = len(rstat)
+        cdef int* c_cstat = <int*> malloc(ncols * sizeof(int))
+        cdef int* c_rstat = <int*> malloc(nrows * sizeof(int))
+        cdef int i
+
+        for i in range(ncols):
+            c_cstat[i] = cstat[i]
+        for i in range(nrows):
+            c_rstat[i] = rstat[i]
+
+        PY_SCIP_CALL(SCIPlpiSetBase(self.lpi, c_cstat, c_rstat))
+
+        free(c_rstat)
+        free(c_cstat)
+
     # Parameter Methods
 
     def setIntParam(self, param, value):

src/pyscipopt/scip.pxd

@@ -1532,6 +1532,8 @@ cdef extern from "scip/scip.h":
     SCIP_RETCODE SCIPlpiGetPrimalRay(SCIP_LPI* lpi, SCIP_Real* ray)
     SCIP_RETCODE SCIPlpiGetDualfarkas(SCIP_LPI* lpi, SCIP_Real* dualfarkas)
     SCIP_RETCODE SCIPlpiGetBasisInd(SCIP_LPI* lpi, int* bind)
+    SCIP_RETCODE SCIPlpiGetBase(SCIP_LPI* lpi, int* cstat, int* rstat)
+    SCIP_RETCODE SCIPlpiSetBase(SCIP_LPI* lpi, const int* cstat, const int* rstat)
     SCIP_RETCODE SCIPlpiGetRealSolQuality(SCIP_LPI* lpi, SCIP_LPSOLQUALITY qualityindicator, SCIP_Real* quality)
     SCIP_RETCODE SCIPlpiGetIntpar(SCIP_LPI* lpi, SCIP_LPPARAM type, int* ival)
     SCIP_RETCODE SCIPlpiGetRealpar(SCIP_LPI* lpi, SCIP_LPPARAM type, SCIP_Real* dval)

src/pyscipopt/scip.pyi

@@ -467,6 +467,7 @@ class LP:
     def delCols(self, firstcol: Incomplete, lastcol: Incomplete) -> Incomplete: ...
     def delRows(self, firstrow: Incomplete, lastrow: Incomplete) -> Incomplete: ...
     def getActivity(self) -> Incomplete: ...
+    def getBase(self) -> Incomplete: ...
     def getBasisInds(self) -> Incomplete: ...
     def getBounds(
         self, firstcol: Incomplete = ..., lastcol: Incomplete = ...
@@ -491,6 +492,7 @@ class LP:
     def ncols(self) -> Incomplete: ...
     def nrows(self) -> Incomplete: ...
     def readLP(self, filename: Incomplete) -> Incomplete: ...
+    def setBase(self, cstat: Incomplete, rstat: Incomplete) -> Incomplete: ...
     def setIntParam(self, param: Incomplete, value: Incomplete) -> Incomplete: ...
     def setRealParam(self, param: Incomplete, value: Incomplete) -> Incomplete: ...
     def solve(self, dual: Incomplete = ...) -> Incomplete: ...

tests/test_lp.py

@@ -89,3 +89,21 @@ def test_lp():
 
     assert round(myLP.getObjVal() == solval)
     assert round(5.0 == solval)
+
+    # test basis get/set
+    binds = myLP.getBasisInds()
+    assert len(binds) == myLP.nrows()
+
+    cstat, rstat = myLP.getBase()
+    assert len(cstat) == myLP.ncols()
+    assert len(rstat) == myLP.nrows()
+
+    # set the same basis back and re-solve
+    myLP.setBase(cstat, rstat)
+    solval2 = myLP.solve()
+    assert round(solval2, 10) == round(solval, 10)
+
+    # verify basis is preserved after set
+    cstat2, rstat2 = myLP.getBase()
+    assert cstat2 == cstat
+    assert rstat2 == rstat