Implemented Thomas Algorithm in Lua (#522)

Author: Vexatos

CONTRIBUTORS.md

@@ -38,4 +38,5 @@ This file lists everyone, who contributed to this repo and wanted to show up her
 - PaddyKe
 - nic-hartley
 - crafter312
-- Christopher Milan
+- Christopher Milan
+- Vexatos

contents/thomas_algorithm/code/lua/thomas.lua

@@ -0,0 +1,35 @@
+function thomas(a, b, c, d)
+
+  -- Create tables and set initial elements
+  local c_prime = {c[1] / b[1]}
+  local result = {d[1] / b[1]}
+
+  for i = 2, #a do
+    -- Scale factor is for c_prime and result
+    local scale = 1.0 / (b[i] - a[i] * c_prime[i - 1])
+    c_prime[i] = c[i] * scale
+    result[i] = (d[i] - a[i] * result[i - 1]) * scale
+  end
+
+  -- Back-substitution
+  for i = #a-1, 1, -1 do
+    result[i] = result[i] - (c_prime[i] * result [i + 1])
+  end
+
+  return result
+end
+
+local a = {0.0, 2.0, 3.0}
+local b = {1.0, 3.0, 6.0}
+local c = {4.0, 5.0, 0.0}
+local d = {7.0, 5.0, 3.0}
+
+print("The system")
+print(b[1], c[1], "",   "|", d[1])
+print(a[2], b[2], c[2], "|", d[2])
+print("",   a[3], b[3], "|", d[3])
+print("Has the solution:")
+
+local solution = thomas(a, b, c, d)
+
+print(table.unpack(solution))

contents/thomas_algorithm/thomas_algorithm.md

@@ -121,6 +121,8 @@ You will find this algorithm implemented [in this project](https://scratch.mit.e
 [import, lang:"nim"](code/nim/thomas_algorithm.nim)
 {% sample lang="cpp" %}
 [import, lang:"c_cpp"](code/c++/thomas.cpp)
+{% sample lang="lua" %}
+[import, lang:"lua"](code/lua/thomas.lua)
 {% endmethod %}
 
 <script>