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Mathematics Algebra Wolfram Language Symbolic Computations

Converting sum of logarithms to the logarithm of a product?

Posted 9 years ago

I know there is some sort of external function to convert Log[x]+Log[y] into Log[x y] but cannot find it. Any help?

POSTED BY: Robert Curl

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Posted 9 years ago

Thanks for the help. Both ideas look good. Bob

POSTED BY: Robert Curl

Posted 9 years ago

You can do it with Simplify with assumptions Simplify[Log[x] + Log[y], x > 0 && y > 0] or with a replacement rule: logRule = a_. Log[x_] + b_. Log[y_] :> Log[x^a*y^b]; Log[x] + Log[y] - Log[3] //. logRule Beware that the rule has restrictions on its valididy.

POSTED BY: Gianluca Gorni

Posted 9 years ago

Greetings Bob, from Sy Blinder The rule for sum of logs doesn't appear to be built in to Mathematica. But try the following workaround: In[13]:= Log[Exp[Log[x] + Log[y]]] Out[13]= Log[x y]

POSTED BY: S M Blinder

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