Fixed #1013: simplify wrongly simplifing some expressions containin…

…g unary minus, like `0 - -x`

HISTORY.md

@@ -9,6 +9,8 @@
   instead of `f(x, y, z)`. Thanks @joelhoover.
 - Fixed `simplify` throwing an error in some cases when simplifying unknown
   functions, for example `simplify('f(4)')`. Thanks @joelhoover.
+- Fixed #1013: `simplify` wrongly simplifing some expressions containing unary
+  minus, like `0 - -x`. Thanks @joelhoover.
 - Fixed an error in an example in the documentation of `xor`. Thanks @denisx.
 
 

lib/function/algebra/simplify/util.js

@@ -31,9 +31,6 @@ function factory(type, config, load, typed, math) {
   }
 
   function isAssociative(node, context) {
-    if (!node.args || node.args.length <=1) {
-      return true;
-    }
     var name = node.fn.toString();
     if (context && context.hasOwnProperty(name) && context[name].hasOwnProperty('associative')) {
       return context[name].associative;

test/function/algebra/simplify.test.js

@@ -82,6 +82,16 @@ describe('simplify', function() {
       assert.equal(result, "x + y - 1");
   });
 
+  it('should simplify convert minus and unary minus', function() {
+    // see https://github.com/josdejong/mathjs/issues/1013
+    assert.equal(math.simplify('0 - -1', {}).toString(), '1');
+    assert.equal(math.simplify('0 - -x', {}).toString(), 'x');
+    assert.equal(math.simplify('0----x', {}).toString(), 'x');
+    assert.equal(math.simplify('1 - -x', {}).toString(), 'x + 1');
+    assert.equal(math.simplify('0 - (-x)', {}).toString(), 'x');
+    assert.equal(math.simplify('-(-x)', {}).toString(), 'x');
+    assert.equal(math.simplify('0 - (x - y)', {}).toString(), 'y - x');
+  });
 
   it('should handle custom functions', function() {
     function doubleIt (x) { return x + x }