Expose lp basis methods

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 ### Added
+- Added `getBase()` and `setBase()` methods to `LP` class for getting/setting basis status
 - Added `getMemUsed()`, `getMemTotal()`, and `getMemExternEstim()` methods
 ### Fixed
 - Removed `Py_INCREF`/`Py_DECREF` on `Model` in `catchEvent`/`dropEvent` that caused memory leak for imbalanced usage

src/pyscipopt/__init__.py

@@ -28,6 +28,7 @@
 from pyscipopt.scip      import LP as LP
 from pyscipopt.scip      import IISfinder as IISfinder 
 from pyscipopt.scip      import PY_SCIP_LPPARAM as SCIP_LPPARAM
+from pyscipopt.scip      import PY_SCIP_BASESTAT as SCIP_BASESTAT
 from pyscipopt.scip      import readStatistics as readStatistics
 from pyscipopt.scip      import Expr as Expr
 from pyscipopt.scip      import MatrixExpr as MatrixExpr

src/pyscipopt/lp.pxi

@@ -531,6 +531,66 @@ cdef class LP:
 
         return binds
 
+    def getBase(self):
+        """Returns the basis status of columns and rows.
+
+        Status values are defined in SCIP_BASESTAT: LOWER, BASIC, UPPER, ZERO.
+
+        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.
+
+        Status values are defined in SCIP_BASESTAT: LOWER, BASIC, UPPER, ZERO.
+
+        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 = self.ncols()
+        cdef int nrows = self.nrows()
+        if len(cstat) != ncols:
+            raise ValueError(f"cstat has length {len(cstat)}, expected {ncols}")
+        if len(rstat) != nrows:
+            raise ValueError(f"rstat has length {len(rstat)}, expected {nrows}")
+        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.pxi

@@ -118,6 +118,12 @@
     POLISHING      = SCIP_LPPAR_POLISHING
     REFACTOR       = SCIP_LPPAR_REFACTOR
 
+cdef class PY_SCIP_BASESTAT:
+    LOWER = SCIP_BASESTAT_LOWER
+    BASIC = SCIP_BASESTAT_BASIC
+    UPPER = SCIP_BASESTAT_UPPER
+    ZERO  = SCIP_BASESTAT_ZERO
+
 cdef class PY_SCIP_PARAMEMPHASIS:
     DEFAULT      = SCIP_PARAMEMPHASIS_DEFAULT
     CPSOLVER     = SCIP_PARAMEMPHASIS_CPSOLVER
@@ -316,7 +322,7 @@
     if rc == SCIP_OKAY:
         pass
     elif rc == SCIP_ERROR:
         raise Exception('SCIP: unspecified error!')
     elif rc == SCIP_NOMEMORY:
         raise MemoryError('SCIP: insufficient memory error!')
     elif rc == SCIP_READERROR:
@@ -335,7 +341,7 @@
         raise Exception('SCIP: method cannot be called at this time'
                             + ' in solution process!')
     elif rc == SCIP_INVALIDDATA:
         raise Exception('SCIP: error in input data!')
     elif rc == SCIP_INVALIDRESULT:
         raise Exception('SCIP: method returned an invalid result code!')
     elif rc == SCIP_PLUGINNOTFOUND:

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: ...
@@ -1801,6 +1803,13 @@ class PY_SCIP_LOCKTYPE:
     MODEL: ClassVar[int] = ...
     def __init__(self) -> None: ...
 
+class PY_SCIP_BASESTAT:
+    LOWER: ClassVar[int] = ...
+    BASIC: ClassVar[int] = ...
+    UPPER: ClassVar[int] = ...
+    ZERO: ClassVar[int] = ...
+    def __init__(self) -> None: ...
+
 class PY_SCIP_LPPARAM:
     BARRIERCONVTOL: ClassVar[int] = ...
     CONDITIONLIMIT: ClassVar[int] = ...

tests/test_lp.py

@@ -1,5 +1,6 @@
 from pyscipopt import LP
 from pyscipopt import SCIP_LPPARAM
+from pyscipopt import SCIP_BASESTAT
 
 def test_lp():
     # create LP instance, minimizing by default
@@ -89,3 +90,25 @@ 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()
+    assert all(s in (SCIP_BASESTAT.LOWER, SCIP_BASESTAT.BASIC,
+                     SCIP_BASESTAT.UPPER, SCIP_BASESTAT.ZERO) for s in cstat)
+    assert all(s in (SCIP_BASESTAT.LOWER, SCIP_BASESTAT.BASIC,
+                     SCIP_BASESTAT.UPPER) for s in rstat)
+
+    # 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