# Tagged Questions

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### Rewriting the matrix equation $AX = YB$ as $Y = CX$?

Is it possible in general, if $A,B,C,X,Y$ are square and of the same dimensions? If so, does it generalize to non-square matrices (using a pseudoinverse)? I'm doing some curve fitting in which I have ...
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### Linear system of equations and multiple linear regression: Numerical solving

I am currently implementing a test procedure for data, namely a linear form of the Kramers-Kronig relations (paper here: http://jes.ecsdl.org/content/142/6/1885.abstract). This includes solving a ...
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### Smallest set of Liner equations, which exactly fit a set of points

I have a set of 2-d points,(it can be of any arbitrary dimension n). I want to find the minimum set of straight lines(linear equations) which exactly passes through the given 2-d points (unlike ...
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### Least Squares “analytic expression” for fitting a 2D quadratic function to measurements

I have n scattered elevation measurements: $\{x_i,y_i,z_i\}_{i=1..n}$ that I want to fit a quadratic function to: $z = ax^2 + by^2 + cxy + dx + ey + f$. The problem can be written as a vector ...
### Derivative of $H$ with respect to $W$
I am trying to solve a generalized linear squares model with the following form: $\hat{Y}= X(X'\Omega^{-1}WX)^{-1}X'\Omega^{-1}WY$ $H= X(X'\Omega^{-1}WX)^{-1}X'\Omega^{-1}W$ $\Omega$ is the ...