From: Todd Benson <caduceass@...>
Date: 2007-07-12T23:18:28+09:00
Subject: Re: matrix problem

On 7/12/07, Bulhac Mihai <mihai.bulhac@yahoo.com> wrote:
> i have a matrix :remember=Matrix[ []     ]
> and this line remember[0,0]=3
> why do i have this error at that line:  undefined method `[]=' for
> Matrix[[]]:Matrix (NoMethodError)
>
> and how do i set values for my matrix only with one row

Hmm.  It appears Matrix objects are supposed to be immutable.  Use
arrays instead and convert to Matrix for matrix-type functions, so ...

irb> require 'matrix'
=> true
irb> require 'mathn' #need this for correct determinant calculations
=> true
irb> a = [[1, 2], [3, 4]]
=> [[1, 2], [3, 4]]
irb> a[0][0] = 3
=> [[3, 2], [3, 4]]
irb> m = Matrix[*a]
=> Matrix[[3, 2], [3, 4]]
irb> m.transpose
=> Matrix[[3, 3], [2, 4]]
irb> m * m
=> Matrix[[15, 14], [21, 22]]
irb> m_float = m.map {|i| i.to_f}
=> Matrix[[3.0, 2.0], [3.0, 4.0]]
irb> m_inv = m_float.inverse
=> Matrix[[0.666666666666667, -0.333333333333333], [-0.5, 0.5]]
irb> m.to_a
=> [[0.666666666666667, -0.333333333333333], [-0.5, 0.5]]

hth,
Todd