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Re: Initialize a matrix in mathematica
*To*: mathgroup at smc.vnet.net
*Subject*: [mg66768] Re: Initialize a matrix in mathematica
*From*: Bill Rowe <readnewsciv at earthlink.net>
*Date*: Mon, 29 May 2006 06:06:38 -0400 (EDT)
*Sender*: owner-wri-mathgroup at wolfram.com
On 5/28/06 at 6:08 AM, ashesh.cb at gmail.com (ashesh) wrote:
>Have programmed in another system until now and am trying to shift
>to Mathematica and facing some diffciulties
>I would like to create a matrix, say a[ndiv] and would like to
>initilize all the value to i^2 (or any other value). The size of the
>matrix is not fixed.
>The code I tried to use is:
>ndiv = 5; a = {}; For[i=1, i<=ndiv, i++, a[[i]] = i*i;
>];
>a
>This is producing the following error: partw: Part 1 of {} does not
>exist and so on.
>I understand that I am not creating a matrix of size 1*ndiv for the
>data to be fed it.
>So I tried using Table as follows:
>a = Table[0,{1},{ndiv}] followed by the above For loop (when I
>wanted to initialize the matrix with say i*i;
I am not entirely clear as to what you are trying to create. You say matrix which usually means a 2 dimensional array. Yet the code you provide clearly has only one dimension
Your first attempt doesn't work as you would like since you define a to be an empty list. Hence the error message. You could do what you want using a For loop with Append, i.e.,
In[1]:=
ndiv=5;
a={};
For[i=1,iâ?¤ndiv,i++,a=Append[a,i*i];];
a
Out[4]=
{1,4,9,16,25}
But while this works, it isn't an efficient way to create this list. Better would be:
In[5]:=
Table[i^2,{i,ndiv}]
Out[5]=
{1,4,9,16,25}
and even simpler is
In[6]:=
Range[ndiv]^2
Out[6]=
{1,4,9,16,25}
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