added multiplication matrices

src/main/scala/info/schleichardt/math/ValueMatrix.scala

@@ -1,5 +1,8 @@
 package info.schleichardt.math
 
+import collection.{Seq, GenTraversableOnce}
+import collection.immutable.IndexedSeq
+
 object ValueMatrix {
   def apply(input: Seq[Double]*) = new ValueMatrix(input)
 }
@@ -58,4 +61,22 @@ class ValueMatrix(val content: Seq[Seq[Double]]) {
       }
     new ValueMatrix(seq)
   }
+
+  lazy val isNullMatrix: Boolean = {
+    val allInALine: Seq[Double] = content.flatMap(x => x)
+    allInALine.forall(_ == 0)
+  }
+
+  def *(other: ValueMatrix): ValueMatrix = {
+    require(columnCount == other.content.length, "length matches")
+    val seq: Seq[Seq[Double]] =
+      for (lineResult <- 0 until content.length) yield {
+        for (columnResult <- 0 until content(0).length) yield {
+          (for (column <- 0 until content(0).length) yield {
+            content(lineResult)(column) * other.content(column)(columnResult)
+          }).sum
+        }
+      }
+    new ValueMatrix(seq)
+  }
 }

src/test/scala/MatrixSpec.scala

@@ -16,5 +16,23 @@ class MatrixSpec extends Specification with JUnit with ScalaTest {
       val transposedMatrix = matrix.transpose
       transposedMatrix must_== ValueMatrix(Seq(1, 1), Seq(-3, 2), Seq(2, 7))
     }
+    "be null matrices" in {
+      val nullMatrix = ValueMatrix(Seq(0, 0, 0), Seq(0, 0, 0), Seq(0, 0, 0))
+      val notNullMatrix = ValueMatrix(Seq(1, 0, 2), Seq(1, 2, 7))
+      nullMatrix.isNullMatrix must be_==(true)
+      notNullMatrix.isNullMatrix must be_==(false)
+    }
+    "be multiplied" in {
+      val left = ValueMatrix(Seq(0, 1, 2), Seq(4, 2, 3), Seq(5, 3, 1))
+      val right = ValueMatrix(Seq(3, 1, 1), Seq(1, 3, 1), Seq(4, 0, 2))
+      left * right must be_==(ValueMatrix(Seq(9, 3, 5), Seq(26, 10, 12), Seq(22, 14, 10)))
+    }
+    "only fitting matrices can be multiplied" in {
+      val matrixWith3Rows = ValueMatrix(Seq(0, 1, 2), Seq(4, 2, 3), Seq(5, 3, 1))//3 rows, 3 columns
+      val matrixWith2Rows = ValueMatrix(Seq(3, 1, 1), Seq(1, 3, 1))//2 rows, 3 columns
+      matrixWith3Rows * matrixWith2Rows must throwA[IllegalArgumentException]
+      matrixWith2Rows * matrixWith3Rows must not(throwA[IllegalArgumentException])
+    }
+
   }
 }