Problem 1197. Numerical Integration

Created by Tomasz

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{"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>Input</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"ListParagraph\"/><w:numPr><w:numId w:val=\"1\"/></w:numPr></w:pPr><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>x0</w:t></w:r><w:r><w:t>, a real number greater than 0</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Output</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"ListParagraph\"/><w:numPr><w:numId w:val=\"1\"/></w:numPr></w:pPr><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>I</w:t></w:r><w:r><w:t>, a numerical estimate of the integral</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[      x0\n      /\n  I = |  cosh(x) / sqrt(cosh(x0) - cosh(x)) dx\n      /\n      0]]></w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Example:</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[   x0=1.0  -->  I = 2.6405789412796]]></w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Remarks:</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"ListParagraph\"/><w:numPr><w:numId w:val=\"1\"/></w:numPr></w:pPr><w:r><w:t>Aim at a relative precision better than 1e-10</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"ListParagraph\"/><w:numPr><w:numId w:val=\"1\"/></w:numPr></w:pPr><w:r><w:t>The problem arises studying the frictionless movement of a mass point on a hanging wire, which follows the curve cosh(x).</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>"}]}

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93 Solutions
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Last Solution submitted on Jun 23, 2020

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2 Comments

Rafael S.T. Vieira on 17 Jun 2020

Please, add to the problem description that for values smaller than one, we should use 1 + x^2/2 for approximating the integrand. For instance, the answer provided by vpaintegral (Symbolic Math Toolbox; commented in my solution) is not accepted by the 4th test case: I believe that vpaintegral returns the exact solution*. The precision for the 4th test should be way smaller, 1e-2/1e-3, or the problem description needs to be changed.

* vpaintegral can handle values that cause the MATLAB integral function to overflow or underflow.

Rafael S.T. Vieira on 17 Jun 2020

As a sanity check, I even did Monte Carlo Integration for the 4th case, and it still did not work, because the problem is not asking for the exact solution, but an approximation of an approximation (and that's why the requested precision should be smaller).

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