# Replace[] malfunction?

Posted 9 years ago
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 The replacement operation below doesn't work properly, i.e. not all the the sigmas are changed.Why?
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Posted 9 years ago
 I wanted to try and find a less nested expression. Here is another (visually cleaner) attempt where f[x] is the original expression on which the operation needs to be implemented. ((FullForm[f[x]] /. Power[#1, #2] -> #3) /. Power[#1, -#2] -> #3^-1) &[(*Variable to be replaced*)x,(*power \ of variable to be replaced*)2,(*The replacing variable*)k] 
Posted 9 years ago
 interesting
Posted 9 years ago
 A given power might exist as Power[x,2] (which becomes k) or Power[x, -2] (which we want to become k^-1). Therefore we might try the following on the FullForm, since FullForm makes expressions look like lists. The replacements are done for all levels down to Infinity. (* Mathematica 7 *) FullForm[(*given equation*)] Replace[ (* First replacement for all [Sigma]^2 *) Replace[%, #, Infinity(*Close inner Replace[]*)] &[Power[[Sigma], 2] -> [Kappa]], (* Second replacement for all [Sigma]^-2 *) #, Infinity] &[ Power[[Sigma], -2] -> [Kappa]^-1 (*Close outer Replace[]*)] 
Posted 9 years ago
 E.g., (-(a/(2 s^2))) // FullForm returns Times[Rational[-1,2],a,Power[s,-2]] which does not match s^2
Posted 9 years ago
 I am having a hard time posting what I want to. However my suggestion is to see what the FullForm of the expression is. your sigma^2 may not appear in that form in both places, but your replacement rule only covers the specific pattern that you use
Posted 9 years ago
 There is just the likelihood function of the normal distribution with a replacement rule.I like to work with greeks in Mathematica :), so if you copy the LaTeX code below in the online editor: http://www.codecogs.com/latex/eqneditor.php, you will get the picture. \left(2 \pi \sigma ^2\right)^{-\frac{n}{2}} \exp \left(-\frac{\sum _{i=1}^n \left(x_i-\theta \right){}^2}{2 \sigma ^2}\right)\text{/.}\, \sigma ^2\to \kappa 
Posted 9 years ago
 It seems that the image that you tried to upload did not appear. Perhaps post the code?