Index: /issm/trunk-jpl/src/c/classes/Loads/Friction.cpp
===================================================================
--- /issm/trunk-jpl/src/c/classes/Loads/Friction.cpp	(revision 18991)
+++ /issm/trunk-jpl/src/c/classes/Loads/Friction.cpp	(revision 18992)
@@ -42,9 +42,22 @@
 void Friction::GetAlphaComplement(IssmDouble* palpha_complement, Gauss* gauss){/*{{{*/
 
+	switch(this->law){
+		case 1:
+			GetAlphaViscousComplement(palpha_complement,gauss);
+			break;
+		case 3:
+			GetAlphaHydroComplement(palpha_complement,gauss);
+			break;
+	  default:
+			_error_("not supported");
+	}
+
+}/*}}}*/
+
+void Friction::GetAlphaViscousComplement(IssmDouble* palpha_complement, Gauss* gauss){/*{{{*/
+
 	/* FrictionGetAlpha2 computes alpha2= drag^2 * Neff ^r * vel ^s, with Neff=rho_ice*g*thickness+rho_ice*g*bed, r=q/p and s=1/p. 
 	 * FrictionGetAlphaComplement is used in control methods on drag, and it computes: 
 	 * alpha_complement= Neff ^r * vel ^s*/
-
-	if(this->law!=1)_error_("not supported");
 
 	/*diverse: */
@@ -104,4 +117,64 @@
 }
 /*}}}*/
+void Friction::GetAlphaHydroComplement(IssmDouble* palpha_complement, Gauss* gauss){/*{{{*/
+
+	/*diverse: */
+	IssmDouble  q_exp;
+	IssmDouble  C_param;
+	IssmDouble  As;
+	IssmDouble  Neff;
+	IssmDouble  n;
+	IssmDouble  alpha;
+	IssmDouble  Chi;
+	IssmDouble  vx,vy,vz,vmag;
+	IssmDouble  alpha_complement;
+
+	/*Recover parameters: */
+	element->GetInputValue(&q_exp,FrictionQEnum);
+	element->GetInputValue(&C_param,FrictionCEnum);
+	element->GetInputValue(&As,FrictionAsEnum);
+
+	element->GetInputValue(&Neff,gauss,FrictionEffectivePressureEnum);
+	element->GetInputValue(&n,gauss,MaterialsRheologyNEnum);
+
+	if(Neff<0)Neff=0;
+
+	//We need the velocity magnitude to evaluate the basal stress:
+	switch(dim){
+		case 1:
+			element->GetInputValue(&vx,gauss,VxEnum);
+			vmag=sqrt(vx*vx);
+			break;
+		case 2:
+			element->GetInputValue(&vx,gauss,VxEnum);
+			element->GetInputValue(&vy,gauss,VyEnum);
+			vmag=sqrt(vx*vx+vy*vy);
+			break;
+		case 3:
+			element->GetInputValue(&vx,gauss,VxEnum);
+			element->GetInputValue(&vy,gauss,VyEnum);
+			element->GetInputValue(&vz,gauss,VzEnum);
+			vmag=sqrt(vx*vx+vy*vy+vz*vz);
+			break;
+		default:
+			_error_("not supported");
+	}
+	if (q_exp==1){
+		alpha=1;
+	}
+	else{
+		alpha=(pow(q_exp-1,q_exp-1))/pow(q_exp,q_exp);
+	}
+	Chi=vmag/(pow(C_param,n)*pow(Neff,n)*As);
+
+	/*Check to prevent dividing by zero if vmag==0*/
+	if(vmag==0.) alpha_complement=0.;
+	else if(Neff==0.) alpha_complement=0.;
+	else alpha_complement=-(C_param*Neff/(vmag*n)) * pow((Chi/(alpha*pow(Chi,q_exp)+1)),((1-n)/n)) *(Chi/(As*(alpha*pow(Chi,q_exp)+1)))-(alpha*q_exp*pow(Chi,q_exp+1)/(As*(alpha*pow(Chi,q_exp)+1)));
+	_assert_(!xIsNan<IssmDouble>(alpha_complement));
+	/*Assign output pointers:*/
+	*palpha_complement=alpha_complement;
+}
+/*}}}*/
 void Friction::GetAlpha2(IssmDouble* palpha2, Gauss* gauss){/*{{{*/
 
@@ -191,5 +264,4 @@
 	}
 	Chi=vmag/(pow(C_param,n)*pow(Neff,n)*As);
-
 
 	/*Check to prevent dividing by zero if vmag==0*/
Index: /issm/trunk-jpl/src/c/classes/Loads/Friction.h
===================================================================
--- /issm/trunk-jpl/src/c/classes/Loads/Friction.h	(revision 18991)
+++ /issm/trunk-jpl/src/c/classes/Loads/Friction.h	(revision 18992)
@@ -30,4 +30,6 @@
 		void  Echo(void);
 		void  GetAlphaComplement(IssmDouble* alpha_complement,Gauss* gauss);
+		void  GetAlphaViscousComplement(IssmDouble* alpha_complement,Gauss* gauss);
+		void  GetAlphaHydroComplement(IssmDouble* alpha_complement,Gauss* gauss);
 		void  GetAlpha2(IssmDouble* palpha2,Gauss* gauss);
 		void  GetAlpha2Hydro(IssmDouble* palpha2,Gauss* gauss);