code simplification, and correct treatment of units

/********************stomatal resistance****************************/

StomatalResistance::StomatalResistance(SimulaDynamic* const pSV) :

		DerivativeBase(pSV), cachedTime(-10), temperature(25), pressure(101325) {

		DerivativeBase(pSV), cachedTime(-10), temperature(25), pressure(101325), invert(false) {

	//check if unit given in input file agrees with this function

	pSD->checkUnit("s/m");

	std::string name = pSD->getName().substr(0, 6); // name = sunlit or shaded

	bool splitBySunStatus(false);

	if (name == "sunlit" || name == "shaded"){

		splitBySunStatus = true;

		name.at(0) = std::toupper(name.at(0));

		stomatalConductance_ = pSD->existingSibling("mean" + name + "StomatalConductance", "mol/m2/s");

	}else{

		stomatalConductance_ = pSD->existingSibling("meanStomatalConductance","mol/m2/s");

	}

	//check if unit given in input file agrees with this function

	pSD->checkUnit("s/m");

	if (splitBySunStatus) stomatalConductance_ = pSD->existingSibling("mean" + name + "StomatalConductance", "mol/m2/s");

	else stomatalConductance_ = pSD->existingSibling("meanStomatalConductance","mol/m2/s");

	if (stomatalConductance_){

		airTemperature_ = pSD->existingPath("/environment/atmosphere/averageDailyTemperature", "degreesC");

		pressure_ = pSD->existingPath("/atmosphere/airPressure", "Pa");

		if (!airTemperature_) msg::warning("StomatalResistance: Air temperature not found, defaulting to 25 degrees C");

		if (!pressure_) msg::warning("StomatalResistance: Air pressure not found, defaulting to 101325 Pa");

	}

	}else{

		dailyBulkStomatalResistance_ = pSD->existingSibling("dailyBulkStomatalResistance");

	if(!dailyBulkStomatalResistance_) msg::warning("StomatalResistance: dailyBulkStomatalResistance as sibling of "+pSD->getPath()+"not found, using default value of 100 m/s");

	leafAreaIndex_ 				 = pSD->getSibling("meanLeafAreaIndex"); //, "m/s"

		if(!dailyBulkStomatalResistance_) {

			msg::warning("StomatalResistance: dailyBulkStomatalResistance as sibling of "+pSD->getPath()+"not found, using default value of 100 s/m. Consider defining meanStomatalConductance in mol/m2/s.");

		}else{

			dailyBulkStomatalResistance_->checkUnit("s/m");

		}

	}

	leafAreaIndex_ = pSD->getSibling("meanLeafAreaIndex");

}

std::string StomatalResistance::getName() const {

//		leaf temperature, and vapor pressure gradient ( Jarvis, 1976, Stewart, 1989 and Price and Black, 1989)

//		and rl increases with environmental stresses such as soil moisture deficit

//		( Stewart, 1988, Stewart and Verma, 1992 and Hatfield and Allen, 1996).

// TODO coupling

		double r_l(100.); // default value, (m/s) is the daily bulk stomatal resistance of the well-illuminated (single) leaf

		double r_l(100.); // default value, (s/m)

		// The bulk stomatal resistance, rl, is the average resistance of an individual leaf,

		// and has a value of about 100 s/m under well-watered conditions.

		// and has a value of about 1/100 s/m under well-watered conditions.

		// TODO could be fitted to a crop average?

		if (dailyBulkStomatalResistance_){

			dailyBulkStomatalResistance_->get(t, r_l);

		}

		double LAI = 3;

		leafAreaIndex_->get(t,LAI);

		double lai_active;

		if(LAI > 0.8/0.3)

			lai_active = 0.5 * LAI;

		else if(LAI >= 1){

			lai_active = LAI / (0.3 * LAI+ 1.2);

		}else{

			lai_active=1./1.5;

		}

		// greater resistance (more conductance) when LAI is larger

		const double frac=std::min(2.0,std::max(1.5,0.3*LAI+1.2));

		// the active (sunlit) leaf area index, which takes into consideration

		/// the fact that generally only the upper half of dense clipped grass

		/// is actively contributing to the surface heat and vapour transfer.

		/// If the crop is not transpiring at a potential rate, the resistance depends also on the water status of the vegetation.

		/// An acceptable approximation to a much more complex relation of the surface resistance of dense full cover vegetation is:

		//

		r_s = r_l / lai_active;

		r_s = r_l * frac;

		//

		// This procedure also presents difficulties. Firstly, evaporation losses from soil must be

		// negligible. If not, r_s will not be representative of total evaporation losses.

	SimulaBase *stomatalConductance_, *airTemperature_, *pressure_, *dailyBulkStomatalResistance_, *leafAreaIndex_;

	double cachedTime, temperature, pressure;

	bool invert;

};