Re: Special Matrix
- To: mathgroup at smc.vnet.net
- Subject: [mg28342] Re: Special Matrix
- From: "Carl K. Woll" <carlw at u.washington.edu>
- Date: Thu, 12 Apr 2001 02:18:06 -0400 (EDT)
- Organization: University of Washington
- References: <9ah5nq$ps0@smc.vnet.net> <9ajmap$s9e@smc.vnet.net> <9b0sso$rq@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi Allan, If further speed improvements are sought, one of the slowest parts of both functions in your post is the use of Table. A faster way of creating this table is to again use PadLeft, as in In[3]:= t1[n_]:=Table[1,{n},{n}] t2[n_]:=PadLeft[{{}},{n,n},1] In[5]:= Do[t1[100], {1000}]; // Timing Do[t2[100], {1000}]; // Timing t1[100] === t2[100] Out[5]= {11.719 Second, Null} Out[6]= {5.578 Second, Null} Out[7]= True Carl Woll Physics Dept U of Washington "Allan Hayes" <hay at haystack.demon.co.uk> wrote in message news:9b0sso$rq at smc.vnet.net... > Souvik, > Here is another way > > PM1[n]:= > Block[{mat= Table[1,{n},{n}]},mat[[{1,-1},All]]=0;mat[[All,{1,-1}]]=0;mat] > > It seems to be slightly quicker than Carl Woll's (which itself appears to be > the fastest of the posting so far) > > PM2[n_]:=PadLeft[Table[1,{n-2},{n-2}],{n,n},0,{1,1}] > > n=2000; > > M1= PM1[n];//Timing > > {8.18 Second,Null} > > M2= PM2[n];//Timing > > {10.71 Second,Null} > > Check > > M1===M2 > > True > > -- > Allan > --------------------- > Allan Hayes > Mathematica Training and Consulting > Leicester UK > www.haystack.demon.co.uk > hay at haystack.demon.co.uk > Voice: +44 (0)116 271 4198 > Fax: +44 (0)870 164 0565 > > "Souvik Banerjee" <s-banerjee at nwu.edu> wrote in message > news:9ajmap$s9e at smc.vnet.net... > > Not sure if the shortest but it works: > > > > CreateMatrix[n_] := > > Block[{r,c,m}, > > Needs["LinearAlgebra`MatrixManipulation`"]; > > r = ZeroMatrix[1, n]; m = Table[1, {n - 2}, {n - 2}]; > > c = ZeroMatrix[n - 2, 1]; > > BlockMatrix[{{r}, {c, m, c}, {r}}] > > ] > > > > The bottleneck seems to be the Table[] operations. If there is a built in > > function to create a matrix with a constant element then it will speed > this > > up. > > > > -Souvik > > > > > > Yoram Pollack <syftech at saad.org.il> wrote in message > > news:9ah5nq$ps0 at smc.vnet.net... > > > Hello > > > I am trying to create a "n x n" matrix with "1" in every position exept > in > > > first and last row, and first and last coulumn, where "0" is needed. In > > > other words: sqare matrix full of "1" sorounded by "0". > > > What will be the fastest and shortest way to do it? > > > > > > Thanks > > > Yoram > > > > > > > > > > > > > > > > > >