Silly question on Matrices
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From: Eduardo M. A. M.Mendes on 4 Aug 2010 05:51 Hello there I am new to Mathematica. In one of my attempts to understand how it works, I tried the following example A={{1,2,3},{4,5,6},{7,8,9}} //MatrixForm The result seems to be a matrix 3x3 but when I try A[[1][1]], the whole first line shows up instead of just one element. If I don't use MatrixForm, it works fine. How can I see a matrix in nice format without wrecking everything? Many thanks Ed
From: David Park on 4 Aug 2010 07:34 I would usually write that as: (amat = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}) // MatrixForm amat[[1]][[1]] amat[[1, 1]] David Park djmpark(a)comcast.net http://home.comcast.net/~djmpark/ From: Eduardo M. A. M.Mendes [mailto:emammendes(a)gmail.com] Hello there I am new to Mathematica. In one of my attempts to understand how it works, I tried the following example A={{1,2,3},{4,5,6},{7,8,9}} //MatrixForm The result seems to be a matrix 3x3 but when I try A[[1][1]], the whole first line shows up instead of just one element. If I don't use MatrixForm, it works fine. How can I see a matrix in nice format without wrecking everything? Many thanks Ed
From: Peter Pein on 4 Aug 2010 07:44 Am Wed, 4 Aug 2010 09:51:07 +0000 (UTC) schrieb "Eduardo M. A. M.Mendes" <emammendes(a)gmail.com>: > Hello there > > I am new to Mathematica. In one of my attempts to understand how it > works, I tried the following example > > A={{1,2,3},{4,5,6},{7,8,9}} //MatrixForm > > The result seems to be a matrix 3x3 but when I try A[[1][1]], the > whole first line shows up instead of just one element. If I don't > use MatrixForm, it works fine. How can I see a matrix in nice format > without wrecking everything? > > Many thanks > > Ed > > Do not assign MatrixForm[{{<matrix>}}] to a but {{<matrix>}} and throw MatrixForm onto A: In[11]:= (A={{1,2,3},{4,5,6},{7,8,9}})//MatrixForm Out[11]//MatrixForm= ( 1 2 3 4 5 6 7 8 9 ) In[12]:= A[[1,1]] (* A[[1][1]] is wrong *) Out[12]= 1 hth, Peter
From: Bob Hanlon on 4 Aug 2010 08:18 Use parentheses to exclude MatrixForm from the definition of A (A = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}) // MatrixForm A[[1, 1]] 1 A[[1]][[1]] 1 Bob Hanlon ---- "Eduardo M. A. M.Mendes" <emammendes(a)gmail.com> wrote: ============= Hello there I am new to Mathematica. In one of my attempts to understand how it works, I tried the following example A={{1,2,3},{4,5,6},{7,8,9}} //MatrixForm The result seems to be a matrix 3x3 but when I try A[[1][1]], the whole first line shows up instead of just one element. If I don't use MatrixForm, it works fine. How can I see a matrix in nice format without wrecking everything? Many thanks Ed
From: Bill Rowe on 5 Aug 2010 06:59
On 8/4/10 at 5:50 AM, emammendes(a)gmail.com (Eduardo M. A. M.Mendes) wrote: >I am new to Mathematica. In one of my attempts to understand how it >works, I tried the following example >A={{1,2,3},{4,5,6},{7,8,9}} //MatrixForm >The result seems to be a matrix 3x3 but when I try A[[1][1]], the >whole first line shows up instead of just one element. If I don't >use MatrixForm, it works fine. How can I see a matrix in nice >format without wrecking everything? My recommendation is Go to preferences. Select the evaluation tab. Then, use the menu to set the format for new output cells to be TraditionalForm from the menu. This will cause the display of all matrices to have a pretty form that you like without the need for MatrixForm. The problem with MatrixForm is that it does two things. It causes the display to be what you want. But it also adds a wrapper to the matrix being displayed. That is, In[1]:= a = RandomInteger[10, {2, 2}] Out[1]= {{5, 4}, {2, 5}} In[2]:= MatrixQ[a] Out[2]= True In[3]:= b = MatrixForm[a]; MatrixQ[b] Out[4]= False MatrixForm will not change the way arguments supplied to it evaluate. This is what is meant when the documentation says MatrixForm does not effect evaluation. But the output of MatrixForm is not a matrix and cannot be used as a matrix directly. |