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: Pi in component TempR
 * Undefined: Po in component TempR
 * Undefined: Qi in component TempR
 * Undefined: Qo in component TempR
 * Undefined: R in component TempR
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.