Use of unassigned parameters in Mathcad I want to define a function with parameters and make calculations with it so that the resulting equations contain my parameters and are not calculated based on the pre-defined values of parameters.
Consider I have some function with 2 parameters (a,b) in a Mathcad document.
When I type something like:
$$f(t):=at^2+bt+5$$
I get an error claiming that variable a is undefined. When I use $\rightarrow$ transformation in the same statement I see something like:
$$f(t):=at^2+bt+5 \rightarrow at^2+bt+5 $$
which looks like a duplication of my statement (I anticipate some mistake here) but generates no error.
When I then do calculations with $f(t)$, for example to get $f(1)$, I get the proper parameteric equations like:
$$f(1)=a+b+5$$
 - AND THIS IS WHAT I REALLY WANT AS A RESULT.
If I define some values for $a:=10$ and $b:=20$ before declaration of $f(t)$, I get $f(1)$ calculated with that values:
$$f(1)=35$$
- WHICH IS NOT A RESULT I WANT, but in such case I get no error when I don't use $\rightarrow$ in $f(t)$ declaration!
Am I doing these operations right or is there some other way to define parameters before declaring $f(t)$ formula to get PARAMETER-based calculations for $f(1)$ and do not using $\rightarrow$ transformation in $f(t)$ statement?
 A: You will get the 'undefined variable' error because the variable is, well... undefined.  
In Mathcad, if you declare a function that uses variables that have not been previsouly defined - either as parameters to the function or variables in their own right, then you will get the 'undefined variable' error.
The $ \to $ operator (Evaluate Symbolically) will simply repeat your function as there is nothing to evaluate, and therefore there will be no error.
Your options are:


*

*Define the variables $ \{a,b\} $ before the function declaration and then call the function passing the parameter $ t $

*Create additional parameters to the function for $ \{a,b\} $ and pass these when calling $ f $


What you will have for each option above is a worksheet as follows:
For 1)
$$\begin{align}
& a:=10\\
& b:=20\\
& f(t):=a*t^2+b*t+5\to 10*t^2+20*t+5\\
& f(1)=35
\end{align}$$
For 2)
$$\begin{align}
& a:=10\\
& b:=20\\
& f(a,b,t):=a*t^2+b*t+5\to a*t^2+b*t+5\\
& f(a,b,1)=35
\end{align}$$
Or
$$\begin{align}
& f(a,b,t):=a*t^2+b*t+5\to a*t^2+b*t+5\\
& f(10,20,1)=35
\end{align}$$
I hope this helps and answers the question you have.  If not, please leave me a message or contact me and I will try to help some more.
