Problem 292. Infernal Recursion

Created by Matt Fig

Solve Later

{"relationships":[{"relationshipType":"http://schemas.mathworks.com/matlab/code/2013/relationships/document","targetMode":"","relationshipId":"rId1","target":"/matlab/document.xml"},{"relationshipType":"http://schemas.mathworks.com/matlab/code/2013/relationships/output","targetMode":"","relationshipId":"rId2","target":"/matlab/output.xml"}],"parts":[{"partUri":"/matlab/document.xml","relationship":[],"contentType":"application/vnd.mathworks.matlab.code.document+xml","content":"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<w:document xmlns:w=\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\"><w:body><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Consider the recursion relation:</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>x_n = (x_(n-1)*x_(n-2))^k</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Given x_1, x_2, and k, x_n can be found by this definition. Write a function which takes as input arguments x_1, x_2, n and k. The output should be x_n.</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>For example, if x_1=exp(1), x_2=pi, n=5, and k=5/9 then:</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[R = get_recurse(exp(1),pi,5,4/9)\n\nR =\n      2.31187497992966]]></w:t></w:r></w:p></w:body></w:document>"},{"partUri":"/matlab/output.xml","contentType":"text/xml","content":"<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\" ?><embeddedOutputs><metaData><evaluationState>manual</evaluationState><layoutState>code</layoutState><outputStatus>ready</outputStatus></metaData><outputArray type=\"array\"/><regionArray type=\"array\"/></embeddedOutputs>"}]}

Solve

Solution Stats

156 Solutions
72 Solvers

Last Solution submitted on Mar 01, 2021

Last 200 Solutions

Problem Comments

4 Comments

4 Comments

Show 1 older comment

@bmtran (Bryant Tran) on 9 Feb 2012

is there a story as to why this is "infernal"?

Matt Fig on 9 Feb 2012

I hate recursion, so it is all infernal to me! Iteration is the way to go...

David Young on 29 Feb 2012

Test suite could helpfully include n=1 and n=2 tests. I thought that it needed extra complexity to handle these, but @bmtran's top solution shows it doesn't.

Aurelien Queffurust on 12 Jun 2012

I spend a lot of time to get the correct R from the example. The issue is that you say k = 5/9 instead of 4/9 . Just a typo to correct . Thanks

Solution Comments

Solution 654037

2 Comments

2 Comments

bainhome on 16 Apr 2015

cheat this one because I think my answer wasn't wrong despite the stupidity, wonder if why this insanely slow.

bainhome on 16 Apr 2015

"Recursion" in title had me in a really tricky detour.

Solution 86964

1 Comment

1 Comment

Binbin Qi on 9 May 2012

it cost much too time,so .....

Solution 37119

1 Comment

1 Comment

David Young on 29 Feb 2012

Fails for both n=1 and n=2?

Solution 34698

2 Comments

2 Comments

@bmtran (Bryant Tran) on 9 Feb 2012

holy moly, you posted this one mere seconds after i posted mine.

David Young on 29 Feb 2012

Fails for n=1?

Solution 34697

2 Comments

2 Comments

Alfonso Nieto-Castanon on 9 Feb 2012

that was a photo-finish :)

David Young on 29 Feb 2012

OK for both n=1 and n=2.

Problem Recent Solvers72

Problem Tags

recursion

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Problem 292. Infernal Recursion

Solution Stats

Last 200 Solutions

Problem Comments

Solution Comments

Problem Recent Solvers72

Suggested Problems

More from this Author6

Problem Tags

Community Treasure Hunt

Problem 292. Infernal Recursion

Solution Stats

Last 200 Solutions

Problem Comments

Solution Comments

Problem Recent Solvers72

Suggested Problems

More from this Author6

Problem Tags

Community Treasure Hunt

Players