add performance warnings for conditional var/cov

spleaf/__init__.py

@@ -699,6 +699,15 @@ class Spleaf():
       Full covariance matrix (if calc_cov is True).
     var : (n,) ndarray
       Main diagonal of the covariance matrix (if calc_cov is 'diag').
+
+    Warnings
+    --------
+    While the computational cost of the conditional mean scales as
+    :math:`\mathcal{O}(n)`,
+    the computational cost of the variance scales as
+    :math:`\mathcal{O}(n^2)`,
+    and the computational cost of the full covariance scales as
+    :math:`\mathcal{O}(n^3)`.
     """
 
     u = self.solveLT(self.solveL(y)/self.D)
@@ -762,6 +771,15 @@ class Spleaf():
       Full covariance matrix (if calc_cov is True).
     var : (n2,) ndarray
       Main diagonal of the covariance matrix (if calc_cov is 'diag').
+
+    Warnings
+    --------
+    While the computational cost of the conditional mean scales as
+    :math:`\mathcal{O}(n+n_2)`,
+    the computational cost of the variance scales as
+    :math:`\mathcal{O}(n n_2)`,
+    and the computational cost of the full covariance scales as
+    :math:`\mathcal{O}(n n_2^2)`.
     """
 
     u = self.solveLT(self.solveL(y)/self.D)

spleaf/rv.py

@@ -484,6 +484,15 @@ class Cov(Spleaf):
       Full covariance matrix (if calc_cov is True).
     var : (n2,) ndarray
       Main diagonal of the covariance matrix (if calc_cov is 'diag').
+
+    Warnings
+    --------
+    While the computational cost of the conditional mean scales as
+    :math:`\mathcal{O}(n+n_2)`,
+    the computational cost of the variance scales as
+    :math:`\mathcal{O}(n n_2)`,
+    and the computational cost of the full covariance scales as
+    :math:`\mathcal{O}(n n_2^2)`.
     """
 
     n2 = t2.size