I find myself trying to calculate the compressibility factor of natural gas based on the procedure of calculating the attached document and check if the template is crafted correctly with a given example therein. I do not know how I'm doing it is the most appropriate because I am newbie using M15, but in trying to solve a system of equations I get one of the variables is not defined.
Hope you can help me and if there is something ridiculous in the preparation of such return please hagamenlo know.
Error messages from solve blocks are useless. No matter what the problem is, you always get an undefined variable error.
A trivial substitution reduces your problem to one equation with one unknown. That makes it easy to find the real problem, which is that there is no solution. There is no value of D that results in the expression on the rhs being equal to your target pressure.
Richard're absolutely right, I have committed any error in equations or other part of the file, since according to the document in which this calculation is based there is a value of "D" for this data.