From 29fca794b5d88671a902cff6c2cf4aef643fca23 Mon Sep 17 00:00:00 2001
From: cj12154 <terezi@pyrope.net>
Date: Fri, 13 Jan 2023 12:09:31 -0500
Subject: [PATCH] add print-equations feature

---
 src/matrix/core.clj | 60 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 59 insertions(+), 1 deletion(-)

diff --git a/src/matrix/core.clj b/src/matrix/core.clj
index 0fc2393..3cc91c1 100644
--- a/src/matrix/core.clj
+++ b/src/matrix/core.clj
@@ -134,10 +134,69 @@
    ((comp println #(pretty-matrix % add-bar)) m)
    m))
 
+(defn fmt-num
+  "Format a number, empty string for 1"
+  [n]
+  (if (= 1 n)
+    ""
+    (str n)))
+
+(defn mid-sign
+  "Format a term as either '+ n' or '- n'"
+  [n]
+  (if (pos? n)
+    (str "+ " (fmt-num n))
+    (str "- " (fmt-num (* -1 n)))))
+
+(defn single-term
+  [val name first]
+  (if (zero? val)
+    ""
+    (str (if first
+           (fmt-num val)
+           (mid-sign val))
+         name))
+  )
+
+; could be generalized
+(defn equation-from-row
+  "Write a pretty equation from one row of an augmented matrix"
+  ([row] (apply equation-from-row row))
+  ([x eq] (str (single-term x "x" true)
+               " = " 
+               eq))
+  ([x y eq] 
+   (let [x (single-term x "x" true)
+         y (single-term y "y" (empty? x))]
+     (str x
+          (if (not-empty x) " ")
+          y
+          (if (not-empty y) " ")
+          "= " eq)))
+  ([x y z eq] 
+   (let [x (single-term x "x" true)
+         y (single-term y "y" (empty? x))
+         z (single-term z "z" (and (empty? x) (empty? y)))]
+     (str x
+          (if (not-empty x) " ")
+          y 
+          (if (not-empty y) " ")
+          z
+          (if (not-empty z) " ")
+          "= " eq))))
+
+(defn print-matrix-equations
+  [m]
+  (do 
+    (last (for [row m]
+      (println (equation-from-row row))))
+    m))
+
 (defn swap [n m] #(swap-rows % n m))
 (defn add [from to] #(add-rows % from to))
 (defn add-mul [n from to] #(add-rows-with-mul % n from to))
 (defn mul [n at] #(mul-row % n at))
+(def print-equations print-matrix-equations)
 
 (defn apply-input
   [m]
@@ -156,7 +215,6 @@
    (pprint-matrix m add-bar)
    (iterate (comp #(pprint-matrix % add-bar) apply-input) m)))
 
-
 (defn -main
   "I don't do a whole lot ... yet."
   [& args]