Integrate a Piecewise funition, stange behaviour
- To: mathgroup at smc.vnet.net
- Subject: [mg53799] Integrate a Piecewise funition, stange behaviour
- From: rik <rikypi_CREPA_SPAMMONE at libero.it>
- Date: Fri, 28 Jan 2005 02:43:42 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
hi, i must evaluate this Integrate[]: int1 = Integrate[f, {w[2], - \[Infinity], \[Infinity]}] where: f = Piecewise[ {{2/355, Inequality[2, LessEqual, w[2], LessEqual, 8] && Inequality[4, LessEqual, w[2] + w[3], LessEqual, 12] && Inequality[5, LessEqual, w[1] + w[2], LessEqual, 10] && w[1] â?¥ 0 && w[3] â?¥ 0}}, 0] if i try to evaluate int, Mathematica (ver 5.1) takes 500-600 Mbyte of ram and, after hours and hours, not arrives to any result :-( But if i apply Reduce to domain like this: red1 = Reduce[Inequality[2, LessEqual, w[2], LessEqual, 8] && Inequality[4, LessEqual, w[2] + w[3], LessEqual, 12] && Inequality[5, LessEqual, w[1] + w[2], LessEqual, 10] && w[1] â?¥ 0 && w[3] â?¥ 0] and then i try to evaluate the follow command: Integrate[2/355 Boole[red1], {w[2], - \[Infinity], \[Infinity]}] Mathematica do the calculation in few seconds!!! Why this behaviour? The two expression, f and "2/355 Boole[red1]", are not equal for the Kernel of Mathematica? Is there a way to predict the complexity of a integral of a Piecewise function? thanks and SORRY for my english Riccardo Piovosi
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