RahulOperator added

src/Engine/RahulOperator.h

+#ifndef RAHULOPERATOR_H
+#define RAHULOPERATOR_H
+#include "Vector.h"
+
+namespace LanczosPlusPlus {
+
+template<typename ComplexOrRealType>
+class RahulOperator {
+
+	enum class Label {IDENTITY, N, SZ, C};
+
+public:
+
+	RahulOperator(PsimagLite::String label, SizeType dof, bool transpose = false)
+	    :  dof_(dof), transpose_(transpose)
+	{
+		label_ = fromString(label);
+	}
+
+	SizeType dof() const { return dof_; }
+
+	// The output of this function should be interpreted as follows.
+	// If the function returns false, bit and result MUST BE ignored
+	// If the function results true, bit is what the bit should be and result
+	// contains the multiplier
+	bool actOn(bool& bit, ComplexOrRealType& result) const
+	{
+		static const ComplexOrRealType zeroPointFive = 0.5;
+		result = 1;
+		const bool bitSaved = bit;
+		switch (label_) {
+		case Label::IDENTITY:
+			return true;
+			break;
+		case Label::N:
+			result = (bitSaved) ? 0 : 1;
+			return true;
+		case Label::SZ:
+			result = (bitSaved) ? -zeroPointFive : zeroPointFive;
+			return true;
+		case Label::C:
+			bit = !bit;
+			return ((bitSaved && !transpose_) || (!bitSaved && transpose_));
+		default:
+			throw PsimagLite::RuntimeError("RahulOperator::actOn internal error\n");
+			break;
+		}
+	}
+
+private:
+
+	static Label fromString(PsimagLite::String l)
+	{
+		if (l == "c") return Label::C;
+		if (l == "identity") return Label::IDENTITY;
+		throw PsimagLite::RuntimeError("RahulOperator: Unknow label " + l + "\n");
+	}
+
+	SizeType dof_;
+	bool transpose_;
+	Label label_;
+};
+}
+#endif // RAHULOPERATOR_H