Function Repository Resource:

# SimplifyRepeatedSubexpressions

Replace repeated subexpressions in an expression with new symbols

Contributed by: Jon McLoone
 ResourceFunction["SimplifyRepeatedSubexpressions"][expr] returns a list of the expr with repeated subexpressions removed, along with the replacement rules used to rewrite them in simpler form.

## Examples

### Basic Examples

Find the repeated term in the expression (a+b+c)3+(a+b+c)2:

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Reconstruct the original expression from the decomposed form:

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### Options

Finding many small common subexpressions may not be helpful:

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Find only the largest with "MinLeafCount":

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### Applications

Remove the discriminant from the quadratic solution equations:

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### Properties and Relations

Reconstruct the original expression from the decomposed form by applying ReplaceAll:

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### Possible Issues

The FullForm of subexpressions must match; in this case no match is found:

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This is because the outermost Plus has four arguments and not just the a, b and c:

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If the input expression contains elements with HoldAll, HoldRest or HoldFirst, the contents will evaluate during the search:

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### Neat Examples

Simplify the order three polynomial solution:

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And the order four polynomial solution:

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## Requirements

Wolfram Language 11.3 (March 2018) or above