Negate constraints with -ve rhs and objectives to be minimised

octachrome · Jun 23, 2014 · 59c02fc · 59c02fc
1 parent 6641ca0
commit 59c02fc
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Showing 3 changed files with 69 additions and 1 deletion.
diff --git a/js/lpParser.js b/js/lpParser.js
@@ -71,7 +71,7 @@ function createLpParser() {
 
     exports.pSignedNum = pThen(mul, pSign, pNum);
 
-    exports.pIneq = pAlt(pLit(Tokens.LE), pLit(Tokens.GE));
+    exports.pIneq = pAlt(pLit(Tokens.LE), pLit(Tokens.GE), pLit(Tokens.EQ));
     exports.pAnonConstraint = pThen3(mkConstraint, pExpr, pIneq, pAlt(pNum, pSignedNum));
     exports.pNamedConstraint = pThen3(nameConstraint, pSat(isAlpha), pLit(Tokens.COLON), pAnonConstraint);
     exports.pConstraint = pAlt(pAnonConstraint, pNamedConstraint);

diff --git a/js/preproc.js b/js/preproc.js
@@ -1,10 +1,35 @@
+function negateExpr(expr) {
+    for (var i = 0; i < expr.length; i++) {
+        var term = expr[i];
+        term.coef = -term.coef;
+    }
+}
+
 function canonical(prob) {
     var nextSlack = 0;
 
+    var objective = prob.objective;
+    if (objective) {
+        if (objective.dir === 'minimise') {
+            objective.dir = 'maximise';
+            negateExpr(objective.expr);
+        }
+    }
+
     var constraints = prob.constraints;
     if (constraints) {
         for (var i = 0; i < constraints.length; i++) {
             var constraint = constraints[i];
+            if (constraint.rhs < 0) {
+                constraint.rhs = -constraint.rhs;
+                negateExpr(constraint.expr);
+                if (constraint.op === '<=') {
+                    constraint.op = '>=';
+                } else if (constraint.op === '>=') {
+                    constraint.op = '<=';
+                }
+            }
+
             if (constraint.op === '<=') {
                 var coef = 1;
             } else if (constraint.op === '>=') {

diff --git a/test/preprocSpec.js b/test/preprocSpec.js
@@ -109,5 +109,48 @@ describe('preproc', function () {
                 ]
             });
         });
+
+        it('should convert a constraint with a negative rhs into one with a positive rhs', function () {
+            var prob = {
+                constraints: [
+                    {
+                        expr: [{sym: 'x', coef: 1}, {sym: 'y', coef: 1}],
+                        op: '<=',
+                        rhs: -14
+                    }
+                ]
+            };
+
+            var can = canonical(prob);
+
+            expect(can).toEqual({
+                constraints: [
+                    {
+                        expr: [{sym: 'x', coef: -1}, {sym: 'y', coef: -1}, {sym: '_s0', coef: -1}],
+                        op: '=',
+                        rhs: 14,
+                        slackVar: '_s0'
+                    }
+                ]
+            });
+        });
+
+        it('should convert a minimisation problem to a minimisation problem', function () {
+            var prob = {
+                objective: {
+                    dir: 'minimise',
+                    expr: [{sym: 'x', coef: 1}, {sym: 'y', coef: -1}]
+                }
+            };
+
+            var can = canonical(prob);
+
+            expect(can).toEqual({
+                objective: {
+                    dir: 'maximise',
+                    expr: [{sym: 'x', coef: -1}, {sym: 'y', coef: 1}]
+                }
+            });
+        });
     });
 });