# Why is there a Simplify command in Mathematica? [closed]

I am pretty new to Mathematica (and programming in general). Often, I use Mathematica to check some results (mainly consisting of linear equations) and I wonder why the equations do not equal 0. Then, (sometimes after 10 minutes or so) I find out that I forgot the Simply command (again). I then put my expression into "Simplify[...]" and get 0. However, I wonder, what is the purpose of this command? Why doesn't Mathematica automatically simplify "simple" expressions? E. g. I have the following expression:

-3 a66 + 2 (-a66 + 2 (2 a66 - a77)) + 2 (2 a66 - a77) + a77 - 2 (-2 a66 + 2 (-a66 + 2 (2 a66 - a77)) + a77)

which, only when using Simplify, reduces to

-a66 + a77

I don't see why any user would prefer the former form. So the only reason I could think of is that simplifying needs a lot of computational power. While this may be the case for "difficult" expressions involving trigonometrical expressions, I can't see why this could be the case here.

My Internet search doesn't give any results on this question and it's hard to imagine no one had this question before.

Note that this is not a rant but I genuinely wonder what the reasoning behind this is.

• The short answer is just what you said: simplifying can cost extra computational power, so you need to tell Mathematica to do it explicitly. The longer answer is that there is a basic difference between evaluation of expressions and manipulation of mathematical formulae. In the end, Mathematica is a programming language: if you want it to do mathematics, you need to use the functions that tell it to do mathematics. Jun 12, 2017 at 13:47
• There is Refine, Simplify, FullSimplify, TrigReduce, TensorReduce, Reduce, PossibleZeroQ. This question is not well posed, after all. I find it a duplicate of What is the difference between a few simplification techniques? Jun 12, 2017 at 13:47
• It does auto-simplify in the most trivial cases, and you will find many complaints on this site about this. There is often value of keeping an expression in a certain form. In non-trivial cases simplification takes a long time (because it is neither a straightforward, nor a well defined task). Finally, you forgot that Mathematica is a programming language, not a machine that answers questions (for that see Wolfram|Alpha). Doing too much automatically is counterproductive when programming specific tasks Jun 12, 2017 at 13:48
• Possible duplicate of What is the difference between a few simplification techniques? Jun 12, 2017 at 13:51
• Thank you for your answers. I am really sorry; I did not know about the many simplification commands. I also did not thought that Mathematica is a programming language - to me, it was presented as a powerful computing tool. However, as at least I find it quite annoying, do you know if there is a trick which tells something like "in this notebook, try for every computation for 1 second if you can simplify it (in the way the Simplify command would do), if it can be simplified, return the simplified expression, if not, do what you usually would do"? Jun 13, 2017 at 10:07

Sometimes over simplification destroys the power form expression which is easier to read than expanded form which Simplify always does. Example (x-10+y)^10 is easier to read than x^10 + .......etc and all other terms.
• It does expands it first and then simplifies it. Something user wants to keep equation in original form with a very little modification. For example, if you have (x-10+y)^10+(x-10)^+10(10+y)^10+(x+y)^3 Jun 13, 2017 at 13:49