Model is unsuitably constrained (i.e. there were still some variables left to be computed, and some unusable equations left over).
At the time of the error, the following variables were found:
* Undefined: Na_ext in component NHE3
* Undefined: Na_int in component NHE3
* Undefined: H_ext in component NHE3
* Undefined: H_int in component NHE3
* Undefined: NH4_ext in component NHE3
* Undefined: NH4_int in component NHE3
* Undefined: J_NHE3_Na in component NHE3
* Undefined: J_NHE3_H in component NHE3
* Undefined: J_NHE3_NH4 in component NHE3
* Undefined: J_NHE3_Na_Max in component NHE3
* Defined: x_T in component NHE3
* Undefined: sigma in component NHE3
* Undefined: P_Na in component NHE3
* Undefined: P_H in component NHE3
* Undefined: P_NH4 in component NHE3
* Defined: P0_Na in component NHE3
* Defined: P0_H in component NHE3
* Defined: P0_NH4 in component NHE3
* Defined: K_Na in component NHE3
* Defined: K_H in component NHE3
* Defined: K_NH4 in component NHE3
* Defined: K_I in component NHE3
* Defined: f_m in component NHE3
* Defined: f_M in component NHE3
* Undefined: alpha_ext_Na in component NHE3
* Undefined: alpha_int_Na in component NHE3
* Undefined: beta_ext_H in component NHE3
* Undefined: beta_int_H in component NHE3
* Undefined: gamma_ext_NH4 in component NHE3
* Undefined: gamma_int_NH4 in component NHE3
The following equations couldn't be used:
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.
* Equation with no id on the apply or math element.