For a heat exchanger modelling, I would like to give different equations into the Matlab, and solve the unknowns with respect to equations' relationship. For example these are different equations, and parameters:
. . .
, and among them for example "Aflow" shall exist in three different equations; but in the first line, Matlab stops due to "undefined variable Aflow". I need Matlab to go over all the equations, and find Aflow itself. How can I handle this?