From 7b2bc2111be3b834518fababf658dc997075d925 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?V=C3=ADt=20Tu=C4=8Dek?= <vit.tucek+sagemath@gmail.com>
Date: Tue, 10 May 2016 19:44:55 +0000
Subject: [PATCH] Fix latex representation for elements of Weyl Algebras

---
 src/doc/en/reference/conf_sub.py  |  0
 src/sage/algebras/weyl_algebra.py | 68 +++++++++++++++++++------------
 2 files changed, 41 insertions(+), 27 deletions(-)
 mode change 100644 => 100755 src/doc/en/reference/conf_sub.py

diff --git a/src/doc/en/reference/conf_sub.py b/src/doc/en/reference/conf_sub.py
old mode 100644
new mode 100755
diff --git a/src/sage/algebras/weyl_algebra.py b/src/sage/algebras/weyl_algebra.py
index bda7479174c..5e1b3ccf73e 100644
--- a/src/sage/algebras/weyl_algebra.py
+++ b/src/sage/algebras/weyl_algebra.py
@@ -209,37 +209,51 @@ def _latex_(self):
             sage: x0,x1,x2,dx0,dx1,dx2 = W.gens()
             sage: latex( ((x0^3-x2)*dx0 + dx1)^2 )
             \frac{\partial^{2}}{\partial x_{1}^{2}}
-             + 2 \frac{\partial^{2}}{\partial x_{0}\partial x_{1}}
-             - 2 \frac{\partial^{2}}{\partial x_{0}\partial x_{1}}
-             + \frac{\partial^{2}}{\partial x_{0}^{2}}
-             - 2 \frac{\partial^{2}}{\partial x_{0}^{2}}
-             + \frac{\partial^{2}}{\partial x_{0}^{2}}
-             + 3 \frac{\partial}{\partial x_{0}}
-             - 3 \frac{\partial}{\partial x_{0}}
+            + 2 x_{0}^{3} \frac{\partial^{2}}{\partial x_{0}\partial x_{1}}
+            - 2 x_{2} \frac{\partial^{2}}{\partial x_{0}\partial x_{1}}
+            + x_{0}^{6} \frac{\partial^{2}}{\partial x_{0}^{2}}
+            - 2 x_{0}^{3} x_{2} \frac{\partial^{2}}{\partial x_{0}^{2}}
+            + x_{2}^{2} \frac{\partial^{2}}{\partial x_{0}^{2}}
+            + 3 x_{0}^{5} \frac{\partial}{\partial x_{0}}
+            - 3 x_{0}^{2} x_{2} \frac{\partial}{\partial x_{0}}
         """
         def term(m):
-            # Variable part
-            R = self.parent()._poly_ring
-            ret = repr( R.sum(R.gen(i)**e for i,e in enumerate(m[0])) )
-            # Differential part
-            m = m[1]
-            total = sum(m)
-            if total == 0:
+            def half_term(m, polynomial=True):
+                R = self.parent()._poly_ring
+                total = sum(m)
+                ret = ''
+                if total == 0:
+                    return '1' 
+                if not polynomial:
+                    if total == 1:
+                        ret += '\\frac{\\partial}{'
+                    else:
+                        ret += '\\frac{\\partial^{' + repr(total) + '}}{'
+                for i, power in enumerate(m):
+                    if power == 0:
+                        continue
+                    name = R.gen(i)
+                    if power == 1:
+                        if polynomial:
+                            ret += latex(name)
+                        else:
+                            ret += '\\partial {0}'.format(latex(name))
+                    else:
+                        if polynomial:
+                            ret += '{0}^{{{1}}}'.format(latex(name), power)
+                        else:
+                            ret += '\\partial {0}^{{{1}}}'.format(latex(name), power)
+                if not polynomial:
+                    ret += '}' # closing \frac
                 return ret
-            ret += ' '
-            if total == 1:
-                ret = '\\frac{\\partial}{'
+            p =  half_term(m[0], True)
+            d =  half_term(m[1], False)
+            if p == '1':
+                return d
+            elif d == '1':
+                return p
             else:
-                ret = '\\frac{\\partial^{' + repr(total) + '}}{'
-            for i, power in enumerate(m):
-                if power == 0:
-                    continue
-                name = R.gen(i)
-                if power == 1:
-                    ret += '\\partial {0}'.format(latex(name))
-                else:
-                    ret += '\\partial {0}^{{{1}}}'.format(latex(name), power)
-            return ret + '}'
+                return p + ' '  + d
         return repr_from_monomials(self.list(), term, True)
 
     # Copied from CombinatorialFreeModuleElement