From: Jose Augusto <jasaugusto@...>
Date: 2006-12-11T09:23:09+09:00
Subject: Re: Complete Newbie - Matrix Question

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Hi

Once I had the same problem and proposed the following functions
to be appended to standard matrix and vector classes (but they
weren't ;-(  ):

#
# Extending standard Matrix and Vector Classes to write directly
#
class Matrix

    # setting one single element
    def []=(i, j, val)
        @rows[i][j] = val
    end

    # setting one row
    def set_row(i,*row)
        case row[0]
            when Vector
                @rows[i] = row[0].to_a
            when Array
                @rows[i] = row[0]
            else    # list of scalars
                @rows[i] = row
        end
    end

    # setting one column
    def set_column(j,*column)
        case column[0]
            when Vector, Array
                @rows.collect{|row|
                    row[j] = column[0][j]
                }
            else
                @rows.collect{|row|
                    row[j] = column[j]
                }
        end
    end

end


class Vector
    # setting one single element
    def []=(i, val)
        @elements[i] = val
    end

    # clear vector
    def Vector.zero(n)
        new(:init_elements, Array.new(n,0),
            copy = false)
    end
end

Hope this helps...

JA



On 12/10/06, Jay <j@somewhere.com> wrote:
>
> Hi Folks,
> This is probably quite easy, but I can't find a Matrix function or way
> to populate a specific element of a matrix with a given value? ie, I
> want to tell that element i,j of matrix.a should be 3
> My code below is a simple test to populate a 5 by 5 matrix from values
> in a CSV text file. The loops etc are messy, but it's just an example.
>
>
> require "mathn"
> i=1
> j=1
> a = Matrix.zero(5)
> File.open("TestData.txt").each do |record|
>     record.split(",").each do |field|
>     field.chomp!
>     if i<5 then
>       Matrix.a(i,j)=field                #      <-------------How do I
> do this line?
>     end
>     if i = 5 then
>       i = 1
>       j=j+1
>     end
>     i=i+1
>    end
> end
> puts a.to_s
>
> Any Help/pointers would be great.
> TIA.
> Jay.
>
>
>
>

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