variance in nada-numpy

nada_numpy/array.py

@@ -948,6 +948,31 @@ def test_shuffle_randomness(vector_size, num_shuffles):
 
         return arr
 
+    def var(self) -> "NadaArray":
+        """
+        Compute the variable of array elements.
+
+        Returns:
+            nadaarray: the variance of array elements
+        """
+
+        # Compute the mean
+        m = self.mean()
+
+        # Initialise the sum to 0
+        sum = Integer(0)
+
+        # compute (x_i - mean)^2
+
+        for v in self.inner:
+            diff = v - m
+            sum += (diff * diff)
+
+        # compute variance
+        var = sum / Integer(self.size)
+
+        return NadaArray(np.array([var]))
+
     def __len__(self):
         """
         Overrides the default behavior of returning the length of the object.

nada_numpy/funcs.py

@@ -78,6 +78,7 @@
     "gelu",
     "silu",
     "shuffle",
+    "var",
 ]
 
 
@@ -1290,3 +1291,18 @@ def test_shuffle_randomness(vector_size, num_shuffles):
                 ```
     """
     return arr.shuffle()
+
+def var(array: NadaArray) -> NadaArray:
+    """
+    Computes the variance of the array elements
+
+    args:
+        array (nadaarray): input array
+
+    returns:
+        nadaarray: the variance of the array elements
+    """
+
+    return array.var()
+
+

tests/nada-tests/nada-project.toml

@@ -200,4 +200,8 @@ prime_size = 128
 
 [[programs]]
 path = "src/shuffle.py"
-prime_size = 128
+prime_size = 128
+
+[[programs]]
+path = "src/variance.py"
+prime_size = 128

tests/nada-tests/src/variance.py

@@ -0,0 +1,16 @@
+from nada_dsl import *
+import nada_numpy as na
+
+def nada_main():
+    parties = na.parties(4)
+
+    a = na.array([4], parties[0], "A", SecretInteger)
+
+    a[0] = SecretInteger(Input("A_0", parties[0]))
+    a[1] = SecretInteger(Input("A_1", parties[1]))
+    a[2] = SecretInteger(Input("A_2", parties[2]))
+    a[3] = SecretInteger(Input("A_3", parties[3]))
+
+    var = a.var()
+
+    return na.output(var, parties[1], "my_output")

tests/nada-tests/tests/variance.yaml

@@ -0,0 +1,9 @@
+---
+program: variance
+inputs:
+  A_0: 3
+  A_1: 3
+  A_2: 3
+  A_3: 3
+expected_outputs:
+  my_output_0: 0

tests/test_all.py

@@ -57,6 +57,7 @@
     "shuffle",
     "array_comparison",
     "private_inverse",
+    "var",
 ]
 
 EXAMPLES = [