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Physics Mathematica

Mathematica 10.0, having problems simplifying simple expressions.

Tigran Khachatrjan

Posted 10 years ago

Basically my mathematica can't simplify a simple expression, DVP can be simplified to sqrt(amh) , which is what I would expect mathematica would give me, (I tried the other functions as well, ''Cancel'', ''Expand'',etc), but I just get the same solution that doesn't look simplified at all, help me plz :D.

POSTED BY: Tigran Khachatrjan

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David Keith

Posted 10 years ago

Here's what I get when giving some assumptions. Otherwise Mathematica must give results which are generally valid. In[1]:= dvp = Sqrt[(Sqrt[(a m)/h^5] Sqrt[a h m])/h]; In[2]:= Simplify[dvp] Out[2]= Sqrt[(a m Sqrt[(a m)/h^5])/Sqrt[a h m]] In[3]:= Simplify[dvp, Assumptions -> Element[_, Reals]] Out[3]= Sqrt[a m]/Abs[h]^(3/2) In[4]:= Simplify[dvp, Assumptions -> {Element[_, Reals], h > 0}] Out[4]= Sqrt[(a m)/h^3]

Here's what I get when giving some assumptions. Otherwise Mathematica must give results which are generally valid.

In[1]:= dvp = Sqrt[(Sqrt[(a m)/h^5] Sqrt[a h m])/h];

In[2]:= Simplify[dvp]

Out[2]= Sqrt[(a m Sqrt[(a m)/h^5])/Sqrt[a h m]]

In[3]:= Simplify[dvp, Assumptions -> Element[_, Reals]]

Out[3]= Sqrt[a m]/Abs[h]^(3/2)

In[4]:= Simplify[dvp, Assumptions -> {Element[_, Reals], h > 0}]

Out[4]= Sqrt[(a m)/h^3]

POSTED BY: David Keith

Marco Thiel

Marco Thiel, University of Aberdeen - Dept. of Physics/Mathematics

Posted 10 years ago

Dear Tigran, I think that the problem is that the expression does not simplify the way you think it simplifies without making additional assumptions. You need to consider cases when the variables are negative or complex numbers etc. I suppose that something similar to what you want happens when you make for example the following assumptions: Simplify[Sqrt[(Sqrt[(a m)/h^5] Sqrt[a h m])/h], Assumptions -> {a > 0, m > 0, h > 0}] That gives This is different from what you expect, but I think that you might have made a mistake there in your calculation. An alternative set of assumptions could be: Simplify[Sqrt[(Sqrt[(a m)/h^5] Sqrt[a h m])/h], Assumptions -> {a \[Element] Reals, m \[Element] Reals, h \[Element] Reals}] or equivalently Simplify[Sqrt[(Sqrt[(a m)/h^5] Sqrt[a h m])/h], Assumptions -> {{a, m, h} \[Element] Reals}] both of which give Hope this helps, M.