Thomas Algorithm in Javascript

contents/thomas_algorithm/code/javascript/thomas.js

@@ -0,0 +1,41 @@
+// note this example is inplace and destructive
+thomas = (a, b, c, d) => {
+
+    // set the initial elements
+    c[0] = c[0] / b[0]
+    d[0] = d[0] / b[0]
+
+    n = d.length // number of equations to solve
+    for (i = 1; i < n; i++) {
+        scale = 1 / (b[i] - c[i-1] * a[i]) // scale factor for c and d
+        c[i] *= scale
+        d[i] = (d[i] - a[i] * d[i-1]) * scale
+    }
+
+    // do the back substitution
+    for (i = n-2; i >= 0; i--) {
+        d[i] -= c[i] * d[i+1]
+    }
+
+    return d
+}
+
+/*
+  example for matrix
+  [1  4  0][x]   [7]
+  [2  3  5][y] = [5]
+  [0  3  6][z]   [3]
+
+                  [.8666]
+  soln will equal [1.533]
+                  [-.266]
+  note we index a from 1 and c from 0
+*/
+
+a = [0, 2, 3]
+b = [1, 3, 6]
+c = [4, 5, 0]
+d = [7, 5, 3]
+
+soln = thomas(a, b, c, d)
+console.log(soln)

contents/thomas_algorithm/thomas_algorithm.md

@@ -127,6 +127,8 @@ You will find this algorithm implemented [in this project](https://scratch.mit.e
 [import, lang:"crystal"](code/crystal/thomas.cr)
 {% sample lang="kotlin" %}
 [import, lang:"kotlin"](code/kotlin/thomas.kt)
+{% sample lang="js" %}
+[import, lang:"javascript"](code/javascript/thomas.js)
 {% endmethod %}
 
 <script>