add linear equation solver

Author: jbytecode

src/main/scala/matrix.scala

@@ -146,3 +146,9 @@ object Matrix:
       for j <- 0 until m do
         for k <- 0 until p do result(i)(j) += a(i)(k) * b(k)(j)
     result
+
+  def mul(a: Mat, b: Vec): Vec = mul(a, makeRowMatrix(b)).flatten
+
+  def solve(A: Mat, b: Vec): Vec = mul(inverse(A), b)
+
+

src/test/scala/testmatrix.scala

@@ -412,4 +412,46 @@ class TestMatrix extends munit.FunSuite {
 
     A.assert(Matrix.elementwise_equal(result, expected, 1e-5))
   }
+  test("Equation solve 1"){
+    val Amat = Array(Array(2.0, 4.0), Array(6.0, 5.0))
+    val bvec = Array(12.0, 60.0)
+    val expected = Array(12.857, -3.428)
+    val result = Matrix.solve(Amat, bvec)
+    A.assert(Matrix.elementwise_equal(result, expected, 1e-3))
+  }
+  test("Equation solve 2"){
+    val Amat = Array(Array(2.0, 1.0), Array(6.0, 0.0))
+    val bvec = Array(12.0, 60.0)
+    val expected = Array(10.0, -8.0)
+    val result = Matrix.solve(Amat, bvec)
+    A.assert(Matrix.elementwise_equal(result, expected, 1e-3))
+  }
+  test("Equation solve 3"){
+    val Amat = Array(Array(2.0, 0.0), Array(6.0, 1.0))
+    val bvec = Array(12.0, 60.0)
+    val expected = Array(6.0, 24.0)
+    val result = Matrix.solve(Amat, bvec)
+    A.assert(Matrix.elementwise_equal(result, expected, 1e-3))
+  }
+  test("Equation solve 4"){
+    val Amat = Array(Array(4.0, 1.0), Array(5.0, 0.0))
+    val bvec = Array(12.0, 60.0)
+    val expected = Array(12.0, -36.0)
+    val result = Matrix.solve(Amat, bvec)
+    A.assert(Matrix.elementwise_equal(result, expected, 1e-3))
+  }
+  test("Equation solve 3x3"){
+    val Amat = Array(
+      Array(2.0, 1.0, 3.0),
+      Array(1.0, 2.0, 4.0),
+      Array(2.0, 2.0, 4.0))
+
+    val b = Array(13.0, 17.0, 18.0)
+
+    val expected = Array(1.0, 2.0, 3.0)
+
+    val result = Matrix.solve(Amat, b)
+
+    A.assert(Matrix.elementwise_equal(result, expected, 1e-3))
+  }
 }