2019-03-07 20:31:40 +0200 received badge ● Famous Question (source) 2018-12-06 19:12:13 +0200 received badge ● Notable Question (source) 2018-05-24 03:07:52 +0200 received badge ● Popular Question (source) 2017-03-30 13:42:53 +0200 commented answer Evaluating symbolic expression, when some variables are finally fixed BTW, more on substituting multiple values is on Substituting multiple values question&answer 2017-03-30 13:31:47 +0200 commented answer Evaluating symbolic expression, when some variables are finally fixed BTW, Solution I found thanks to other sage question&answer problems with sage_eval and eval 2017-03-25 01:20:04 +0200 received badge ● Supporter (source) 2017-03-25 01:09:58 +0200 answered a question Evaluating symbolic expression, when some variables are finally fixed Thanks to other answers, which concentrated on particular example, I wanted to explain better what I'm after (i.e. the general solution), and in that process I've got the answer: I = eval(preparse(str(I))) where str(I) converts the 'I' expression to string preparse(...) preparses the code of expression in the sage style ('^' as power, and so on) eval(...) finally evaluates expression (in particular example: taking into account that R is already set to 3) The code thus would be: V = var('V') R = var('R') I = V/R R = 3 # this is one line representation of possible several lines of code # to compute value in general case. Let's also note that the value can # even be provided externally (read from file, or so) I = eval(preparse(str(I))) plot(I)  and having in mind even more general solution with evaluate() definition: def evaluate(expression): return eval(preparse(str(expression))) V = var('V') R = var('R') I = V/R R = 3 # this is one line representation of possible several lines of code # to compute value in general case. Let's also note that the value can # even be provided externally (read from file, or so) I = evaluate(I) plot(I)  Few days later: There is a small improvement possible - by adding simplify(), and so making the whole thing I = simplify(eval(preparse(str(I)))) Please let know if the code could be more elegant (pythonic or sageonic) and if there are some disadvantages or threads in such solution 2017-03-24 17:58:37 +0200 received badge ● Editor (source) 2017-03-24 15:50:15 +0200 received badge ● Student (source) 2017-03-24 13:24:23 +0200 asked a question Evaluating symbolic expression, when some variables are finally fixed Hello I'm looking for solution when bigger number of variables is in the picture. Simple example: There is relationship I = V/R then we know that R = 3, with that knowledge let's plot I(V) in sage it should look something like: V = var('V') R = var('R') I = V/R R = 3 plot(I)  but above is not working, because in plot(I) I is still V/R not V/3 (knowledge of R=3 is not used), so I'm looking for some operation that turns V/R into V/3, something like I = evaluate(I)  but such evaluate() apparently does not exist there are however two different ways (1) repeat I=V/R after R=3 and in such situation I becomes V/3 as needed (2) I = I(R=R) and with earlier R=3, I also becomes V/3 both however seems for me be solution(s) for simple expression with just few variables, and not good (not as straightforward as hypothetical I = evaluate(I) for more complex expression with several variables. Is such evaluate() or so, available already, and I failed to find it? Is there a (easy) way to implement that proposed evaluate() ?