ACCEPTED SOLUTION
Accepted Solutions
Your solve block uses a lot of variables which are not defined.
They obviously are intermediate variables but when you introduce them you also have to use them in the final "Find" command even though you may not be interested in their values.
An alternative might be to use functions.
Here is a simple example of what I am talking about.
This solve block fails because c is not defined:
We add a guess for c and also add it to the "Find" command even though we are only interested in the values of a and b
And here is what I meant with using functions:
You may define the functions also within the solve block.
Now these are three unknown variables and I have three equations, that means that this should be solvable.... right?
Not necessarily - its not mandatory that there always must be a solution for three equations in three variables.
The error message a solve block will always throw ("This variable is undefined") mostly is meaningless and wrong. You get a better clue about what was going wrong if you use Mathcads trace facility: Right click the red highlighted variable and chose "Trace error" and then "First". In your case we now get the error message "No solution found". So you may want to check your equations and used variable values.
You may also use "MinErr" instead of "Find" but I guess the values are not as expected and if we check the three equations, the first two are fulfilled pretty well but the last one fails badly. May be a sign that it may be a good idea to check all equations.
One additional remark.
I put the values into your equations and changed the names of the three variables to be more clearly for me in the process. This resulted in the following linear system of equations and as you can see, the determinant of the coefficient matrix is zero and this means that (the left hand side of ) these three equations are linearly dependent. So you need an additional equation that is independent from the previous ones and you can replace one of the given equations with it.
Ore more precise - the rank of the matrix of coefficients is 2, but the rank of the extended matrix is 3 (hopefully not just because of rounding errors at the values on the right hand side). This means that the system you had set up has no solution! Chances are that at least one of the equations is faulty.
