Modify Ricci Tensor from christoffel method and add from riemann. Fix…

… indentation

.gitignore

@@ -30,7 +30,7 @@ docs/_build
 # Pycharm editor project files
 .idea
 
-
+# for virtual environment
 venv/
 
 # Floobits project files

src/einsteinpy/symbolic/ricci.py

@@ -1,8 +1,8 @@
 import numpy as np
 import sympy
 
-from .tensor import Tensor
 from .metric import MetricTensor
+from .tensor import Tensor
 
 
 class RicciTensor(Tensor):
@@ -43,25 +43,23 @@ def from_christoffels(cls, chris):
 
         Parameters
         ----------
-        chris : ~einsteinpy.symbolic.ricci.RicciTensor
+        chris : ~einsteinpy.symbolic.christoffel.ChristoffelSymbols
             Christoffel Symbols from which Ricci Tensor to be calculated
 
         """
         arr, syms = chris.tensor(), chris.symbols()
         dims = len(syms)
-        ricci_list = (np.zeros(shape=(dims, dims, dims, dims), dtype=int)).tolist()
-        for i in range(dims ** 4):
-            # t,s,r,n each goes from 0 to (dims-1)
-            # hack for codeclimate. Could be done with 4 nested for loops
-            n = i % dims
+        ricci_list = (np.zeros(shape=(dims, dims), dtype=int)).tolist()
+        for i in range(dims ** 2):
+            # r,t each goes from 0 to (dims-1)
+            # hack for codeclimate. Could be done with 2 nested for loops
             r = (int(i / dims)) % (dims)
-            s = (int(i / (dims ** 2))) % (dims)
-            t = n
+            t = (int(i / (dims ** 1))) % (dims)
 
-            temp = sympy.diff(arr[t, s, n], syms[r]) - sympy.diff(arr[t, r, n], syms[s])
+            temp = sympy.diff(arr[t], syms[r])
             for p in range(dims):
-                temp += arr[p, s, n] * arr[t, p, r] - arr[p, r, n] * arr[t, p, s]
-            ricci_list[t][s][r][n] = sympy.simplify(temp)
+                temp += arr[p, r, p, t]
+            ricci_list[t][r] = sympy.simplify(temp)
         return cls(ricci_list, syms)
 
     @classmethod
@@ -71,13 +69,26 @@ def from_metric(cls, metric):
 
         Parameters
         ----------
-        metric : ~einsteinpy.symbolic.ricci.RicciTensor
-            Ricci Tensor
+        metric : ~~einsteinpy.symbolic.metric.MetricTensor
+            Metric Tensor
 
         """
         rc = RicciTensor.from_metric(metric)
         return cls.from_christoffels(rc)
 
+    @classmethod
+    def from_riemann(cls, riemann):
+        """
+        Get Ricci Tensor calculated from a Metric Tensor
+
+        Parameters
+        ----------
+        metric : ~~einsteinpy.symbolic.metric.MetricTensor
+           Metric Tensor
+
+        """
+        return cls(sympy.tensorcontraction(riemann.tensor(), (0, 2)), riemann.syms)
+
     def symbols(self):
         """
         Returns the symbols used for defining the time & spacial axis

src/einsteinpy/symbolic/tensor.py

@@ -1,6 +1,7 @@
 import numpy as np
 import sympy
 
+
 class Tensor:
     """
     Base Class
@@ -12,7 +13,6 @@ def __getitem__(self, index):
     def __setitem__(self, index, value):
         self.arr[index] = value
 
-
     def __init__(self, arr):
         """
         Constructor and Initializer

src/einsteinpy/symbolic/vaccum_metrics.py

@@ -3,21 +3,18 @@
 from .metric import MetricTensor
 
 
-def SchwarzschildMetric(symbolstr="t r theta phi" ):
+def SchwarzschildMetric(symbolstr="t r theta phi"):
     """
-     Returns  Metric Tensor  of symbols of Schwarzschild Metric.
-
-     Parameters
-     ----------
-     symbolstr : string
+    Returns  Metric Tensor  of symbols of Schwarzschild Metric.
+    Parameters
+    ----------
+    symbolstr : string
          symbols to be used to define schwarzschild space, defaults to 't r theta phi'
-
-     Returns
-     -------
-     Metric Tensor
-
-
-     """
+    Returns
+    -------
+    ~einsteinpy.symbolic.metric.MetricTensor
+    Metric Tensor for Schwarzschild space-time
+    """
     list2d = [[0 for i in range(4)] for i in range(4)]
     syms = sympy.symbols(symbolstr)
     c, a = sympy.symbols("c a")
@@ -31,18 +28,16 @@ def SchwarzschildMetric(symbolstr="t r theta phi" ):
 
 def KerrMetric(symbolstr="t r theta phi"):
     """
-            Returns Metric Tensor of symbols of Kerr metric(BL coordinates) in Plank units : G=1, c=1.
-
-            Parameters
-            ----------
-            symbolstr : string
-                symbols to be used to define kerr space in BL coordinates, defaults to 't r theta phi'
-
-            Returns
-            -------
-            Metric Tensor
-
-            """
+    Returns Metric Tensor of symbols of Kerr metric(BL coordinates) in Plank units : G=1, c=1.
+    Parameters
+    ----------
+    symbolstr : string
+        symbols to be used to define kerr space in BL coordinates, defaults to 't r theta phi'
+    Returns
+    -------
+    ~einsteinpy.symbolic.metric.MetricTensor
+    Metric Tensor for Kerr space-time
+    """
     list2d = [[0 for i in range(4)] for i in range(4)]
     syms = sympy.symbols(symbolstr)
     a, R = sympy.symbols("a R")
@@ -52,16 +47,9 @@ def KerrMetric(symbolstr="t r theta phi"):
     list2d[1][1] = sigma / A
     list2d[2][2] = sigma
     list2d[3][3] = (
-                           (sympy.sin(syms[2]) ** 2)
-                           * (
-                                   (a ** 2 + syms[1] ** 2) ** 2
-                                   - (a ** 2) * (A * (sympy.sin(syms[2]) ** 2))
-                           )
-                   ) / sigma
+        (sympy.sin(syms[2]) ** 2)
+        * ((a ** 2 + syms[1] ** 2) ** 2 - (a ** 2) * (A * (sympy.sin(syms[2]) ** 2)))
+    ) / sigma
     list2d[3][0] = -1 * (R * a * (syms[1])) * (sympy.sin(syms[2]) ** 2) / sigma
     list2d[0][3] = list2d[3][0]
     return MetricTensor(list2d, syms)
-
-
-
-

src/einsteinpy/tests/test_symbolic/test_vaccum_metrics.py

@@ -1,7 +1,7 @@
 import numpy as np
 import sympy
 
-from einsteinpy.symbolic import vaccum_metrics, MetricTensor
+from einsteinpy.symbolic import MetricTensor, vaccum_metrics
 
 
 def schwarzschild_metric():
@@ -16,4 +16,3 @@ def kerr_metric():
     syms = sympy.symbols(symbolstr)
     sch = vaccum_metrics.KerrMetric(syms)
     return sch
-