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Define the domain of symbolic variables for a matrix when solving a system of linear equations?

Posted 1 year ago
POSTED BY: Russell Michael
7 Replies
POSTED BY: Gianluca Gorni

Thanks! If the value of f is changed from f ≠ 0 to -1/10 < f < 1/10, or even f = 0, while keeping the range of the other parameters constant and x as a real number, will this provide a solution to the system of equations?

POSTED BY: Russell Michael

You can try. Good luck!

POSTED BY: Gianluca Gorni

Do you really need the full symbolic solution with all parameters? It seems hard.

POSTED BY: Gianluca Gorni

Yes, I would like to have the solution with all parameters.The solution can be complicated. Anyway, thank you very much for your help!!

POSTED BY: Russell Michael

Your value x=ArcTan[1/b/f]/Pi seems wrong to me. I get this:

{{x -> ConditionalExpression[(
    2 ArcTan[b f + Sqrt[1 + b^2 f^2]])/\[Pi], -(1/2) < b < 1/2 && 
     c > 0]}}
POSTED BY: Gianluca Gorni

Thank you! Your method gives the correct result. However, when I change some parameters to get a new matrix, the solution for x becomes a complex transcendental equation, and it is not possible to get a solution for x. How do I find the solution X to the system of linear equations in this case? The parameters also satisfy -1 < a < 1, -0.5 < b < 0.5, c > 0, f ≠ 0, and 0 < x < 1. Here is the new matrix:

mat={{(-2 + x) Cos[1/2 \[Pi] (-2 + x)] - 
   f (-2 + x) Sin[1/2 \[Pi] (-2 + x)], -f (-2 + x) Cos[
     1/2 \[Pi] (-2 + x)] + (2 - x) Sin[1/2 \[Pi] (-2 + x)], 
  x Cos[(\[Pi] x)/2] - 
   f (-2 + x) Sin[(\[Pi] x)/2], -f (-2 + x) Cos[(\[Pi] x)/2] - 
   x Sin[(\[Pi] x)/2], 0, 0, 0, 
  0}, {(-2 + x) Cos[1/2 \[Pi] (-2 + x)], (2 - x) Sin[
    1/2 \[Pi] (-2 + x)], 
  x Cos[(\[Pi] x)/2], -x Sin[(\[Pi] x)/2], (2 - x) Cos[
    3/2 \[Pi] (-2 + x)], (2 - x) Sin[3/2 \[Pi] (-2 + x)], -x Cos[(
    3 \[Pi] x)/2], -x Sin[(3 \[Pi] x)/2]}, {1/
   2 (-2 + a c - b c) (-2 + x) Cos[1/2 \[Pi] (-2 + x)], 
  1/2 (2 - a c + b c) (-2 + x) Sin[1/2 \[Pi] (-2 + x)], 
  1/2 (-2 + a c - b c) (-1 - (-2 + c - b c)/(2 - a c + b c) + 
     x) Cos[(\[Pi] x)/2], 
  1/2 (2 - a c + b c) (-1 - (-2 + c - b c)/(2 - a c + b c) + 
     x) Sin[(\[Pi] x)/2], (-2 + x) Cos[
    3/2 \[Pi] (-2 + x)], (-2 + x) Sin[
    3/2 \[Pi] (-2 + x)], (-1 + 1/2 (2 - c - a c) + x) Cos[(3 \[Pi] x)/
    2], (-1 + 1/2 (2 - c - a c) + x) Sin[(3 \[Pi] x)/2]}, {Sin[
   1/2 \[Pi] (-2 + x)], Cos[1/2 \[Pi] (-2 + x)], Sin[(\[Pi] x)/2], 
  Cos[(\[Pi] x)/2], Sin[3/2 \[Pi] (-2 + x)], -Cos[3/2 \[Pi] (-2 + x)],
   Sin[(3 \[Pi] x)/2], -Cos[(3 \[Pi] x)/2]}, {0, 1, 0, 1, 0, -1, 
  0, -1}, {-2 + x, 0, x, 0, 2 - x, 0, -x, 0}, {0, 
  1/2 (2 - a c + b c) (-2 + x), 0, 
  1/2 (2 - a c + b c) (-1 + (-2 + c - b c)/(2 - a c + b c) + x), 0, 
  2 - x, 0, 1 + 1/2 (2 - c - a c) - x}, {1/2 (2 - a c + b c) (-2 + x),
   0, 1/2 (2 - a c + b c) (-1 - (-2 + c - b c)/(2 - a c + b c) + x), 
  0, 2 - x, 0, 1 + 1/2 (-2 + c + a c) - x, 0}}
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POSTED BY: Russell Michael
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