Changes to Math class and added Latex class.

* Math now adds $$ if the user doesn't provide them.
* Latex is like Math, but doesn't add delimiters.

IPython/core/display.py

@@ -298,6 +298,13 b' class HTML(DisplayObject):'
 class Math(DisplayObject):
 
     def _repr_latex_(self):
+        s = self.data.strip('$')
+        return "$$%s$$" % s
+
+
+class Latex(DisplayObject):
+
+    def _repr_latex_(self):
         return self.data
 
 

IPython/core/formatters.py

@@ -524,7 +524,8 b' class LatexFormatter(BaseFormatter):'
     this.
 
     The return value of this formatter should be a valid LaTeX equation,
-    enclosed in either ```$``` or ```$$```.
+    enclosed in either ```$```, ```$$``` or another LaTeX equation
+    environment.
     """
     format_type = Unicode('text/latex')
 

docs/examples/notebooks/00_notebook_tour.ipynb

@@ -855,7 +855,7 b''
       "Note that this is *different* from the above examples.  Above we were typing mathematical expressions",
       "in Markdown cells (along with normal text) and letting the browser render them; now we are displaying",
       "the output of a Python computation as a LaTeX expression wrapped by the `Math()` object so the browser",
-      "renders it:"
+      "renders it.  The `Math` object will add the needed LaTeX delimiters (`$$`) if they are not provided:"
      ]
     },
     {
@@ -863,22 +863,59 b''
      "collapsed": false,
      "input": [
       "from IPython.core.display import Math",
-      "Math(r'$F(k) = \\int_{-\\infty}^{\\infty} f(x) e^{2\\pi i k} dx$')"
+      "Math(r'F(k) = \\int_{-\\infty}^{\\infty} f(x) e^{2\\pi i k} dx')"
      ],
      "language": "python",
      "outputs": [
       {
        "latex": [
-        "$F(k) = \\int_{-\\infty}^{\\infty} f(x) e^{2\\pi i k} dx$"
+        "$$F(k) = \\int_{-\\infty}^{\\infty} f(x) e^{2\\pi i k} dx$$"
        ],
        "output_type": "pyout",
-       "prompt_number": 8,
+       "prompt_number": 1,
        "text": [
-        "<IPython.core.display.Math at 0x45840d0>"
+        "<IPython.core.display.Math object at 0x10ad35e90>"
        ]
       }
      ],
-     "prompt_number": 8
+     "prompt_number": 1
+    },
+    {
+     "cell_type": "markdown",
+     "source": [
+      "With the `Latex` class, you have to include the delimiters yourself.  This allows you to use other LaTeX modes such as `eqnarray`:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "from IPython.core.display import Latex",
+      "Latex(r\"\"\"\\begin{eqnarray}",
+      "\\nabla \\times \\vec{\\mathbf{B}} -\\, \\frac1c\\, \\frac{\\partial\\vec{\\mathbf{E}}}{\\partial t} & = \\frac{4\\pi}{c}\\vec{\\mathbf{j}} \\\\",
+      "\\nabla \\cdot \\vec{\\mathbf{E}} & = 4 \\pi \\rho \\\\",
+      "\\nabla \\times \\vec{\\mathbf{E}}\\, +\\, \\frac1c\\, \\frac{\\partial\\vec{\\mathbf{B}}}{\\partial t} & = \\vec{\\mathbf{0}} \\\\",
+      "\\nabla \\cdot \\vec{\\mathbf{B}} & = 0 ",
+      "\\end{eqnarray}\"\"\")"
+     ],
+     "language": "python",
+     "outputs": [
+      {
+       "latex": [
+        "\\begin{eqnarray}",
+        "\\nabla \\times \\vec{\\mathbf{B}} -\\, \\frac1c\\, \\frac{\\partial\\vec{\\mathbf{E}}}{\\partial t} & = \\frac{4\\pi}{c}\\vec{\\mathbf{j}} \\\\   \\nabla \\cdot \\vec{\\mathbf{E}} & = 4 \\pi \\rho \\\\",
+        "\\nabla \\times \\vec{\\mathbf{E}}\\, +\\, \\frac1c\\, \\frac{\\partial\\vec{\\mathbf{B}}}{\\partial t} & = \\vec{\\mathbf{0}} \\\\",
+        "\\nabla \\cdot \\vec{\\mathbf{B}} & = 0 ",
+        "\\end{eqnarray}"
+       ],
+       "output_type": "pyout",
+       "prompt_number": 5,
+       "text": [
+        "<IPython.core.display.Latex object at 0x109a38790>"
+       ]
+      }
+     ],
+     "prompt_number": 5
     },
     {
      "cell_type": "markdown",