Re: Problem when NIntegrate matrix

*To*: mathgroup at smc.vnet.net*Subject*: [mg81346] Re: Problem when NIntegrate matrix*From*: "jf.alcover at gmail.com" <jf.alcover at gmail.com>*Date*: Thu, 20 Sep 2007 03:46:12 -0400 (EDT)*References*: <fcqrrj$2jc$1@smc.vnet.net>

On 19 sep, 11:58, chiron1201 <hua... at cse.buaa.edu.cn> wrote: > Hi all! > > I can not understand why there is a NIntegrate::inum error when I try to evaluate the following code > > TEST = Piecewise[{ > {{{1, 2, 3}, {2, 3, 4}, {3, 4, 5}}, #1 < 0.00}, > {{{2, 3, 4}, {3, 4, 5}, {4, 5, 6}}, #1 >= 0.00}, > }] &; > > NIntegrate[TEST[x], {x, -1, +1}] > > However, I can get the correct result by modifying the code manually. That is > > NIntegrate[{{1, 2, 3}, {2, 3, 4}, {3, 4, 5}}, {x, -1, 0}]+NIntegrate[{{2, 3,4}, {3, 4, 5}, {4, 5, 6}}, {x, 0, 1}] > > However, it is impossible for me to manually split the integration range to thousands of segments. Why this happens? What should I do if I want the first code be evaluated correctly? > > Thanks! Good day, Here is my suggestion : In[1]:=m1={{1, 2, 3}, {2, 3, 4}, {3, 4, 5}}; m2={{2, 3,4}, {3, 4, 5}, {4, 5, 6}}; In[3]:=test[x_]=MapThread[Piecewise[{{#1,x<0.},{#2,x>=0.}}]&,{m1,m2}, 2]; In[4]:=NIntegrate[#,{x,-1,1}]& /@test[x] Out[4]={{3., 5., 7.}, {5., 7., 9.}, {7., 9., 11.}} V.Astanoff