fix: add stabilizer for communalities during rotation

xeofs/utils/rotation.py

@@ -56,7 +56,10 @@ def varimax(
  # Normalize the matrix using square root of the sum of squares (Kaiser)
  h = np.sqrt(np.sum(X * X.conjugate(), axis=1))
  # A = np.diag(1./h) @ A
- X = (1. / h)[:, np.newaxis] * X
+
+ # Add a stabilizer to avoid zero communalities
+ eps = 1e-9
+ X = (1. / (h + eps))[:, np.newaxis] * X
 
  # Seek for rotation matrix based on varimax criteria
  delta = 0.
@@ -138,7 +141,9 @@ def promax(
 
  # Pre-normalization by communalities (sum of squared rows)
  h = np.sqrt(np.sum(X * X.conjugate(), axis=1))
- X = (1. / h)[:, np.newaxis] * X
+ # Add a stabilizer to avoid zero communalities
+ eps = 1e-9
+ X = (1. / (h + eps))[:, np.newaxis] * X
 
  # Max-normalisation of columns
  Xnorm = X / np.max(abs(X), axis=0)