pass matrices via reference to silence compiler errors

How did this every worked?

Source/Simulation.h

@@ -58,8 +58,8 @@ namespace DPsim {
 
 		double getTime() { return mTime; }
 		double getFinalTime() { return mFinalTime; }
-		Matrix getLeftSideVector() { return mSystemModel.getLeftSideVector(); }
-		Matrix getRightSideVector() { return mSystemModel.getRightSideVector(); }
+		Matrix & getLeftSideVector() { return mSystemModel.getLeftSideVector(); }
+		Matrix & getRightSideVector() { return mSystemModel.getRightSideVector(); }
 		Matrix getSystemMatrix() { return mSystemModel.getCurrentSystemMatrix(); }
 		int stepGeneratorTest(Logger& logger, Logger& leftSideVectorLog, Logger& rightSideVectorLog, 
 			BaseComponent* generator, Logger& synGenLogFlux, Logger& synGenLogVolt, Logger& synGenLogCurr, Real fieldVoltage, Real mechPower, 

Source/SystemModel.h

@@ -45,10 +45,10 @@ namespace DPsim {
 		void initialize(Int numNodes, Int numIdealVS);
 		void addSystemMatrix(Matrix systemMatrix);
 
-		Matrix getCurrentSystemMatrix() { return mSystemMatrix; }
-		Matrix getLUdecomp() { return mLuFactored.matrixLU(); }
-		Matrix getRightSideVector() { return mRightSideVector; }
-		Matrix getLeftSideVector() { return mLeftSideVector; }
+		Matrix & getCurrentSystemMatrix() { return mSystemMatrix; }
+		const Matrix & getLUdecomp() { return mLuFactored.matrixLU(); }
+		Matrix & getRightSideVector() { return mRightSideVector; }
+		Matrix & getLeftSideVector() { return mLeftSideVector; }
 		Real getTimeStep() { return mTimeStep; }
 		Real getOmega() { return mSystemOmega; }
 		Int getCompOffset() { return mCompOffset; }

[Steffen Vogel]

I am wondering why I had to change this part here.

• Eigen: 3.2.10 on Fedora 25.

I think we should usually pass all matrices as a (const) reference.