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20170330 13:42:53 +0200  commented answer  Evaluating symbolic expression, when some variables are finally fixed BTW, more on substituting multiple values is on

20170330 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

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20170325 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
The code thus would be: and having in mind even more general solution with evaluate() definition: Few days later:
Please let know if the code could be more elegant (pythonic or sageonic) and if there are some disadvantages or threads in such solution 
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20170324 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)
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 but such evaluate() apparently does not exist there are however two different ways Is such evaluate() or so, available already, and I failed to find it? 