Difficult linear algebra problem

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SUMMARY

The discussion revolves around solving the linear algebra equation A[x1 x2] = I, where A is defined as an operator involving shifting matrices s1 and s2. The user seeks to find a matrix form for A to invert it and obtain the unknown matrices x1 and x2. The conversation highlights the complexity of the problem, particularly when dealing with shifting matrices, which are defined as matrices with non-zero entries only on specific diagonals. The conclusion drawn is that, under certain conditions, the problem may yield infinitely many solutions, making it impossible to solve uniquely.

PREREQUISITES
  • Understanding of linear algebra concepts, particularly matrix operations.
  • Familiarity with shifting matrices and their properties.
  • Basic knowledge of tensor mathematics and matrix dimensions.
  • Experience with matrix inversion techniques.
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  • Research the properties and applications of shifting matrices in linear algebra.
  • Explore tensor mathematics to better understand the representation of multi-dimensional data.
  • Study matrix inversion techniques and their limitations in solving linear equations.
  • Investigate the implications of having infinitely many solutions in linear algebra problems.
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Mathematicians, students of linear algebra, and anyone interested in advanced matrix operations and tensor mathematics will benefit from this discussion.

Klandhee
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Hi, my problem is simple enough to write down but (to me) seems quite difficult to solve.

My equation is as follows

A[x1 x2] = I.

Here I is some known matrix, and A is an operator which applies a shifting matrix and sums. That is A[x1 x2] = s1x1 + s2x2, where s1 and s2 are two shifting matrices (continuously it can be thought of as convolving with a delta function). x1 and x2 are two unknown matrices of the same dimension as I. Ultimately I wish to find a matrix form for A so that I can invert it and obtain x1 and x2

So as you can see [x1 x2] can be thought of as a "stack" of matrices, or a 3D matrix (or a tensor?). However I'm very unfamiliar with the mathematics of tensors so one idea I had was to convert x1 and x2 into columns (i.e., just shopping the matrix into slices and adding one ontop of the other). That way [x1 x2] would be a matrix, and I would have lost no information.

From here, however, I am very confused and not sure where to go.

If anyone has any ideas on what to do (or if this problem is impossible) it would be GREATLY appreciated, thanks!
 
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This doesn't sound like homework so I will assume it's not (and therefore not feel bad about providing a "solution").

I'm not sure exactly what you mean by a shifting matrix. The only definition I know of is matrices which are 0 everywhere except on precisely one diagonal either below or above the main diagonal where they are 1. For instance in the 2x2 case
\left[\begin{array}{cc} 0 & 0 \\ 1 & 0 \end{array} \right], \quad\left[\begin{array}{cc} 0 & 1 \\ 0 & 0 \end{array} \right]
are the shift matrices and in the 3x3 case we have:
\left[\begin{array}{ccc} 0 & 0 & 0 \\ 1 & 0 & 0 \\ 0 & 1 & 0 \end{array} \right], \quad\left[\begin{array}{ccc} 0 & 1 & 0 \\ 0 & 0 & 1 \\ 0 & 0 & 0 \end{array} \right]
If this is the case, then we can easily see that it is impossible to solve in general. For example define:
A[x_1,x_2] = \left[\begin{array}{cc} 0 & 0 \\ 1 & 0 \end{array} \right] x_1 +\left[\begin{array}{cc} 0 & 0 \\ 1 & 0 \end{array} \right]x_2
I = \left[\begin{array}{cc} 0 & 0 \\ 0 & 0 \end{array} \right]
Then we have infinitely many solutions of the form
x_1 = \left[\begin{array}{cc} a & b \\ c & d \end{array} \right] \qquad x_2 = \left[\begin{array}{cc} -a & -b \\ e & f \end{array} \right]
for arbitrary reals a,b,c,d,e,f.
 

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