Re: Define a matrix function with size as argument

*To*: mathgroup at smc.vnet.net*Subject*: [mg71394] Re: Define a matrix function with size as argument*From*: Bill Rowe <readnewsciv at sbcglobal.net>*Date*: Thu, 16 Nov 2006 00:54:08 -0500 (EST)

On 11/15/06 at 6:45 AM, sgiannerini at gmail.com (Simone Giannerini) wrote: >I am quite new to Mathematica and I have the following problem I >could not find track of both in the Forum and in the documentation. >I need to define a matrix function with size of the matrix as an >argument. The function produces a tridiagonal matrix: >Q[w_] := MatrixForm[SparseArray[ >{i_, j_} /; Abs[i - j] <= 1 -> Which[i < j, >a[i - 1]*(1 - (i - 1)/(2*w)), i > j, >(a[-i + 2*w + 1]*(i - 1))/(2*w), i == j, >(-(1 - (i - 1)/(2*w)))*a[i - 1] - >(a[-i + 2*w + 1]*(i - 1))/(2*w) + 1], >{2*w, 2*w}]] >dum = Q[2] >the problem is that dum is not recognized as a matrix so that >operations like Inversion and the like do not work. Don't use MatrixForm in the function Q[w_]. MatrixForm puts a wrapper around the array and is causing your problem. If you prefer (as I do) to see the array displayed in MatrixForm, the best way to achieve this is to set the default output to TraditionalForm and forget the existence of MatrixForm altogether. -- To reply via email subtract one hundred and four