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	FriCAS Problems
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simplifying Expressions

Edit detail for simplifying Expressions revision 2 of 4

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Editor: test1 Time: 2015/05/08 16:23:52 GMT+0
Note:

changed:
-integrate(exp(-x**2/2)/sqrt(2*%pi),x=%minusInfinity..%plusInfinity)
integrate(exp(-x^2/2)/sqrt(2*%pi),x=%minusInfinity..%plusInfinity)

Simplification of Expressions

Suppose we compute

fricas

integrate(exp(-x^2/2)/sqrt(2*%pi),x=%minusInfinity..%plusInfinity)

$\label{eq1}{{\sqrt{2}}\ {\sqrt{\pi}}}\over{\sqrt{2 \ \pi}}$

(1)

Type: Union(f1: OrderedCompletion?(Expression(Integer)),...)

And now I wonder why common factors are not cancelled and why not the result "1" is produced.

In general (unlike some other computer math systems) Axiom automatically performs only a very small number of basic simplifications. This is not one of them, so we need to provide some help. In particular we need to tell Axiom how to expand square roots. (Since $\sqrt{\ }$ is a multi-valued function this rule is true only in a restricted sense for a particular choice of branches. Consider .)

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expandSqrt := rule sqrt(a*b)==sqrt(a)*sqrt(b)

$\label{eq2}{\sqrt{a \ b}}\mbox{\rm = =}{{\sqrt{a}}\ {\sqrt{b}}}$

(2)

Type: RewriteRule?(Integer,Integer,Expression(Integer))

Next, notice that the output of the integration operation has a complicated type structure. This would interfere with the simplification, so we first simplify the type before we apply the rule.

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(%% 1)::Expression Integer

$\label{eq3}{{\sqrt{2}}\ {\sqrt{\pi}}}\over{\sqrt{2 \ \pi}}$

(3)

Type: Expression(Integer)

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expandSqrt %

$\label{eq4}1$

(4)

Type: Expression(Integer)