eja: cache the charpoly coefficients for the AlbertEJA.

[sage.d.git] / mjo / eja / eja_utils.py

diff --git a/mjo/eja/eja_utils.py b/mjo/eja/eja_utils.py
index 7c6c581329dd64aaa8f3d958e00b2f9eb3221fcb..3942e70811c6d69e59c9581d23f17af05c261dfa 100644 (file)
--- a/mjo/eja/eja_utils.py
+++ b/mjo/eja/eja_utils.py
@@ -2,6 +2,40 @@ from sage.functions.other import sqrt
 from sage.matrix.constructor import matrix
 from sage.modules.free_module_element import vector
 
+def _charpoly_sage_input(s):
+    r"""
+    Helper function that you can use on the string output from sage
+    to convert a charpoly coefficient into the corresponding input
+    to be cached.
+
+    SETUP::
+
+        sage: from mjo.eja.eja_utils import _charpoly_sage_input
+
+    EXAMPLES::
+
+        sage: J = JordanSpinEJA(4,QQ)
+        sage: J._charpoly_coefficients()[0]
+        X1^2 - X2^2 - X3^2 - X4^2
+        sage: _charpoly_sage_input("X1^2 - X2^2 - X3^2 - X4^2")
+        'X[0]**2 - X[1]**2 - X[2]**2 - X[3]**2'
+
+    """
+    import re
+
+    exponent_out = r"\^"
+    exponent_in = r"**"
+
+    digit_out = r"X([0-9]+)"
+
+    def replace_digit(m):
+        # m is a match object
+        return "X[" + str(int(m.group(1)) - 1) + "]"
+
+    s = re.sub(exponent_out, exponent_in, s)
+    return re.sub(digit_out, replace_digit, s)
+
+
 def _scale(x, alpha):
     r"""
     Scale the vector, matrix, or cartesian-product-of-those-things