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Alex edited comment on MATH-832 at 7/26/12 9:27 AM: ---------------------------------------------------- I tried testMath832() and there was no error (although i'm not sure if i did it right - i never worked with JUnit before). But now i think i know where the problem is: It isn't the difference between optimizing and solving (minimizing a function (that derivative has only one root) => finding the root of the derivative) but a numerical issue: [http://www.wolframalpha.com/input/?i=Plot(100*sqrt%28x%29%2B1000000%2Fx%2B10000%2Fsqrt%28x%29%2C+{x%2C+0%2C+1000})] asd [http://www.wolframalpha.com/input/?i=Plot(d%2Fdx+100*sqrt%28x%29%2B1000000%2Fx%2B10000%2Fsqrt%28x%29%2C+{x%2C+0%2C+1000})] asd [http://www.wolframalpha.com/input/?i=Plot(d%2Fdx+100*sqrt%28x%29%2B1000000%2Fx%2B10000%2Fsqrt%28x%29%2C+{x%2C+10^10%2C+10^100})] An upper bound for the interval sufficiently smaller than infinity causes no problems:{code:borderStyle=solid} System.out.println( (new BrentSolver()).solve(Integer.MAX_VALUE, uf, 1/Double.MAX_VALUE, *1.0e10*, startValue2) );{code} was (Author: alex87): I tried testMath832() and there was no error (although i'm not sure if i did it right - i never worked with JUnit before). But now i think i know where the problem is: It isn't the difference between optimizing and solving (minimizing a function (that derivative has only one root) => finding the root of the derivative) but a numerical issue: [http://www.wolframalpha.com/input/?i=Plot(100*sqrt%28x%29%2B1000000%2Fx%2B10000%2Fsqrt%28x%29%2C+{x%2C+0%2C+1000})] [http://www.wolframalpha.com/input/?i=Plot(d%2Fdx+100*sqrt%28x%29%2B1000000%2Fx%2B10000%2Fsqrt%28x%29%2C+{x%2C+0%2C+1000})] [http://www.wolframalpha.com/input/?i=Plot(d%2Fdx+100*sqrt%28x%29%2B1000000%2Fx%2B10000%2Fsqrt%28x%29%2C+{x%2C+10^10%2C+10^100})] An upper bound for the interval sufficiently smaller than infinity causes no problems:{code:borderStyle=solid} System.out.println( (new BrentSolver()).solve(Integer.MAX_VALUE, uf, 1/Double.MAX_VALUE, *1.0e10*, startValue2) );{code} > Brent solver calculates incorrect root (namley Double.MAX_VALUE) > ---------------------------------------------------------------- > > Key: MATH-832 > URL: https://issues.apache.org/jira/browse/MATH-832 > Project: Commons Math > Issue Type: Bug > Affects Versions: 3.0 > Environment: Netbeans 7.1.2 > Reporter: Alex > > *Wolfram-Alpha-Solution:* > [http://www.wolframalpha.com/input/?i=min+100*sqrt%28x%29%2B1000000%2Fx%2B10000%2Fsqrt%28x%29+with+x%3E0] > {code:borderStyle=solid}min{100 sqrt(x)+1000000/x+10000/sqrt(x)|x>0}~~4431.94 > at x~~804.936{code} > *Java-Input:*{code:borderStyle=solid} > int startValue1 = 100 + 1000000 + 10000; > int startValue2 = 100; > UnivariateFunction uf = new UnivariateFunction() { > @Override > public double value(double x) { > return 100/(2*Math.sqrt(x)) - 1000000/Math.pow(x,2) - > 10000/(2*Math.pow(x,(double) 3/2)); > } > }; > System.out.println( > (new BrentSolver()).solve(Integer.MAX_VALUE, uf, 1/Double.MAX_VALUE, > Double.MAX_VALUE, startValue1) > ); > System.out.println( > (new BrentSolver()).solve(Integer.MAX_VALUE, uf, 1/Double.MAX_VALUE, > Double.MAX_VALUE, startValue2) > );{code} > *Java-Output:*{code:borderStyle=solid} > 804.9355821866686 > 1.7976931348623157E308 (= Double.MAX_VALUE){code} -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa For more information on JIRA, see: http://www.atlassian.com/software/jira