From 34b945681740c320c3a011326d493d7bd09019f3 Mon Sep 17 00:00:00 2001
From: Thomas Guillermo Albers Raviola <thomas@thomaslabs.org>
Date: Thu, 16 Jul 2026 23:10:26 +0200
Subject: Initial commit

---
 tensors.mac | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
 create mode 100644 tensors.mac

(limited to 'tensors.mac')

diff --git a/tensors.mac b/tensors.mac
new file mode 100644
index 0000000..dea722a
--- /dev/null
+++ b/tensors.mac
@@ -0,0 +1,21 @@
+/* Contract indices in expression */
+
+/* NOTE: buildq works like splicing a list with quasiquote in lisp; escaped
+items are defined at start of quote */
+contr(expr, var) ::= (
+  if listp(var) and length(var) > 1 then
+  block([head, tail],
+    head : first(var),
+    tail : rest(var),
+    buildq([expr, head, tail], sum(contr(expr, tail), head, 1, 4)))
+  elseif listp(var) and length(var) = 1 then
+  block([head],
+    head : first(var),
+    buildq([expr, head], sum(expr, head, 1, 4)))
+  elseif listp(var) then
+  expr
+  else
+  buildq([expr, var], sum(expr, var, 1, 4)))$
+
+/* Differentiate with respect to nth coordinate */
+cdiff(func, coord) := diff(func, ct_coords[coord])$
-- 
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