Implemented Thomas Algorithm in Crystal (#529)

Author: Vexatos

contents/thomas_algorithm/code/crystal/thomas.cr

@@ -0,0 +1,41 @@
+def thomas(a, b, c, d)
+  c_prime = c.dup
+  x = d.dup
+
+  # Setting initial elements
+  c_prime[0] /= b[0]
+  x[0] /= b[0]
+
+  1.upto(a.size - 1) do |i|
+    # Scale factor is for c_prime and x
+    scale = 1.0 / (b[i] - c_prime[i - 1]*a[i])
+    c_prime[i] *= scale
+    x[i] = (x[i] - a[i] * x[i - 1]) * scale
+  end
+
+  # Back-substitution
+  (a.size - 2).downto(0) do |i|
+    x[i] -= (c_prime[i] * x[i + 1])
+  end
+
+  x
+end
+
+def main
+  a = [0.0, 2.0, 3.0]
+  b = [1.0, 3.0, 6.0]
+  c = [4.0, 5.0, 0.0]
+  d = [7.0, 5.0, 3.0]
+
+  puts "The system"
+  puts [b[0], c[0], "",   "|", d[0]].join("\t")
+  puts [a[1], b[1], c[1], "|", d[1]].join("\t")
+  puts ["",   a[2], b[2], "|", d[2]].join("\t")
+  puts "Has the solution:"
+
+  soln = thomas(a, b, c, d)
+
+  puts soln.join("\t")
+end
+
+main

contents/thomas_algorithm/thomas_algorithm.md

@@ -123,6 +123,8 @@ You will find this algorithm implemented [in this project](https://scratch.mit.e
 [import, lang:"c_cpp"](code/c++/thomas.cpp)
 {% sample lang="lua" %}
 [import, lang:"lua"](code/lua/thomas.lua)
+{% sample lang="crystal" %}
+[import, lang:"crystal"](code/crystal/thomas.cr)
 {% endmethod %}
 
 <script>